Protoscutellidae

Durham, 1955, p.153

Genre type : Protoscutella Stefanini, 1924

Description succinte de la famille : 5 pores génitaux. Sillons nourriciers simples ou bien bifurqués distalement au niveau des premières premières plaques post-basicoronales.

 

 


 

Genre   Protoscutella Stefanini, 1924, p.843

Relations between American and European tertiary echinoid faunas

Espèce type  Scutella mississippiensis Twitchell, 1915 (désignation originale)

Mesozoic and Cenozoic Echinodermata of the United States

Extension stratigraphique (bibliographique, non vérifiée) : Eocène inf (?) à supérieur

 
 
 

Protoscutella conradi (Cotteau,1891)

 
 
description de l'espèce par Clark, 1915
Mesozoic and Cenozoic Echinodermata of the United States, p. 126
 

Scutella (?) conradi (Cotteau).

Plate LXIV, figures 1a-d.

   

     Determinative characters. - Test small in size ; marginal outline subquadrate to suboval, the sides and posterior margin being truncated so that the posterior border is semiquadrate and the anterior border is semicircular ; the whole form much depressed, though centrally it rises in the form of a low gently rounded mound ; margin thin, with a small notch in the middle of the posterior edge ; under surface flat. Ambulacral petals elliptical, extending about halfway to the margin. Apex and apical system central, or slightly excentric anteriorly. Peristome small, subcircular ; ambulacral furrows simple and straight for over halfway to the margin, then becoming obscure. Periproct very small, subpentagonal or subcircular, inframarginal.

     Dimensions. - Length 21 millimeters, width 21 millimeters ; height 3 millimeters. This is Conrad's type, here figured for the first time.

     Description. - The species, though described by Conrad in 1865, has never been figured and is not very well known. There is some doubt in regard to its generic position. Gregory's remark that it should be transferred to the genus Monostychia is not agreed to, for the reason that the type reveals five genital pores and fails to show any continuation of the actinal grooves abactinally. The test is small in size, the type being about 11/36 inch in diameter and about 1/8 inch in height. In marginal outline it is subquadrate to suboval, with the sides and posterior margin truncated so that the posterior half of the border is semiquadrate and the anterior half semi-circular. The upper surface is so much depressed all around the marginal area as to be quite flat, or even slightly concave, but within the area covered by the ambulacral petals it rises in the form of a low, gently rounded mound with a rather broad, flattened summit. The margin is thin, though slightly thicker than the submarginal area, with a small notch in the middle of the posterior side. The under surface is flat. The apex is central or slightly excentric anteriorly, at the summit of the tumid central area.

     The interambulacral areas are relatively large. The whole surface of the test is covered with small uniform tubercles, which are slightly larger on the under side.

     The apical system is subcentral, at the summit of the central mound. The madreporite is relatively large, occupying the larger part of the area covered by the system, and faintly tumid. There are five genital pores near the edge of the madreporite and five small radial plates each perforated by a minute pore.

     The peristome is small, subcircular, central ; the ambulacral furrows simple, straight, and quite distinct for slightly more than half the distance to the margin, then becoming obscure. A small ridge extends from the peristome along the middle of each ambulacral furrow for a greater distance than the diameter of the peristome.

     The periprocte is very small, considerably smaller than the peristome, subpentagonal of sub-circular, situated on the under surface near the posterior margin, being about one-fifth the radius from the border.

     Related forms. - Of American forms S. (?) conradi most closely resembles S. tuomeyi and some of the smaller specimens of Periarchus lyelli, but is easily separated from these species by its subquadrate marginal outline and the inframarginal position of its periproct. It also resembles S. mississippiensis, but its periproct is less nearly marginal. It does not appear closely related to any of the known foreign forms.

     Locality. - Conrad said his type came from near Charleston, S. C.

     Geologic horizon. - Probably Cooper marl, upper Eocene.

     Collection. - Academy of Natural Sciences of Philadelphia (1081).

Planche LXIV (extrait) d'après Clark

   
 

Protoscutella conradi (Cotteau,1891) - Eocène inférieur, Castle Hayne Fm, Duplin Cty, Caroline du Nord, 23 mm

 
 
 

Protoscutella mississippiensis (Twitchell,1915)

 
 
diagnose originale de l'espèce par Twitchell, 1915
Mesozoic and Cenozoic Echinodermata of the United States, p. 124
 

Scutella mississippiensis Twitchell, n. sp.

Plate LIX, figures 1a-f, 2.

     Determinative characters.—Test variable in size; subcircular to subtriangular in marginal outline, broader than long, broadest posteriorly; the whole form greatly depressed, being thin and nearly flat around a narrow marginal area within which it rises very gradually and gently to the low, central apex; margin thin, with a small notch in the middle of the posterior edge; under surface flat. Ambulacral petals elliptical, extending about half way to the margin. Apical system central. Peristome small, circular; ambulacral furrows simple and straight for two-thirds or more of the way to.the margin, thon apparently forking symmetrically. Periproct very small, circular, almost at the ambitus though slightly inframarginal, at the edge of the notch in the middle of the posterior margin.

     Dimensions.—Specimen A: Length 50 millimeters; width 52.5 millimeters; height 6. millimeters. Specimen B: Length 52.5 millitheters; width 76 millimeters; height S millimeters.

     Description.—This new Scutella is one of the most abundant in the American Cenozoic deposits. The writer bas had opportunity to examine several hundred specimens. Neirly all of these were from the Eocene deposits of Mississippi, hence the specific name. The test is variable in size, ranging from less than inch to over 3 inches in diameter and from less than 1/8 to nearly 1/2 inch in height. The marginal outline is also quite variable, ranging from circular to subcircular in the younger forms to subtriangular and even transvcrsely elliptical in the larger forms. The whole form is much depressed, being thin and nearly flat around a narrow marginal area, although slightly more so posteriorly thon elsewhere, from wich it rises gradually and gently to the low, central apex. The margin is thin and faintly undulating, with a small notch in the middle of the posterior edge; the under surface is flat cxcept around the peristome, where it is slightly concave. The apex is central or subcentral, at the summit of the broad central tumid area.

     The ambulacral areas are narrow in the petaloid region but wide in the marginal region where they arc wider thon the interambulacral areas. The dorsal portions of the ambulacra are petaloid. The petals are subequal in length, the odd petal slightly longer and narrower thon the rest; elliptical in form, slightly open at the ends and extencl about half way to the margin. The poriferous zones are rather wide, about equal to the. interporiferous areas, though varying somewhat both among the petals on a single specimen or on different specimens, being slightly wider, equal to, or slightly narrower than the interporiferous areas; the limer row of porcs oval, outer row slitlike, pairs of pores conjugatcd. A few pairs of pores occur beyond the ends of the petals.

     The interambulacral arecs are large though somcwhat smiller both between the petals and et the margin than the ambulacral arecs. The whole surface of the test is covered with small uniform tubercles which are slightly larget. on the under side.

     The apical system is subcentral, at the summit of the central tumid area. The madreporite is relatively large, occupying the langer part of the arec covered by the system, and flush with the surface. There are five genital pores near the edge of the madreporite. One specimen studied possessed the abnormal feature of a double posterior genital pore. There are five small radial plates, each perforated by a minute pore.

     The peristome is very small, not over double the size. of the periproct, circuler, central or slightly excentric posteriorly; the ambulacral furrows simple and straight for two-thircls or more of the distance from peristome to margin, thon apparently forking symmetrically, each pair of branches continuing almost to the margin. The under side is revealed on few specimens, and on few can the furrows be made out.

     The periproct is very small, circuler, almost at the ambitus though slightly inframarginal, situated et the, under and inner edgc of the notch in the middle of the posterior margin.

     Related forms.—S. mississippiensis does not appear to be closely related to any other American form. It resembles Periarchus lyelli, in general appearance, and specimens have doubtless been erroneously labeled S. lyelli, in some collections; S. mississippiensis, however, is readily distinguished by its submarginal periproct, greater width, the notch in its posterior edge, and the fact that its tumid central area involves nearly the whole upper surface. It bears an interesting resemblance to the recent species Scutella parma, but differs from it in having less widely open petals, much narrower interporiferous arecs, a less circuler and more anteriorly pointed form, and in not having its periproct exactly marginal or et the ambitus.

     Of foreign forms S. patagonensis (Desor) Ortman, cspecially the "alate" form described by Ortman and fornierly known as Echinarachnius juliensis Desor from the Neocene of Patagonia, appears to be most closely related to S. mississippiensis. It is very siinilar in marginal outline, location of periproct, etc., but differs in having e less central apical system, longer petals, nar­rower interambulacral arecs, and in having its ambulacral furrows bcghming simply and thon forking in symmetrical curving branches almost immediately. S. subtetragona De Grateloup and S. striatula M. de Serres, both from the upper Eocene of France, aise present certain points of identity with S. mississippiensis. Each, however, differs from the American form in having four genital pores instead of five and in having the ambulacral furrows foré near the peristome.

     Localities.—Cemetery Branch (type), Radiate Banks, Spillman's Clam beel and other localities in and around Enterprise, Clarke County, Miss.; San Augustin, and 1 mile southwest of Palestine, Tex.

     Geologic horizon.—Claiborne group, middle Eocene. In Mississippi, et the base of the Lisbon mari. In Texas, hi the marine substage of the Claiborne.

     Collections.—U. S. National Museum. (137655, A; 137655a, B); Wagner Free Instituts of Science.

Planche LIX (extrait)

   
 
 

Protoscutella mississippiensis (Twitchell,1915) - Eocène, Caroline du Nord, U.S.A., 31 mm

 
 
   
 
 

Protoscutella mississippiensis (Twitchell,1915) - Eocène, Caroline du Nord, U.S.A., 34 mm

 
 
   
 

Protoscutella mississippiensis (Twitchell,1915) - Lutétien, Weches formation, Nacogdoches, Texas, U.S.A., 28 mm

 
 
       
 
 

Protoscutella mississippiensis (Twitchell,1915) - Lutétien, Winona Sand, Enterprise, Clarke Cty, Mississippi, USA, 35 mm