Genre Brissopsis  Agassiz, 1840

Catalogue raisonné des échinides, p.159

Espèce type  Brissus lyrifera Forbes, 1841, A history of british starfishes, and other animals of the class Echinodermata, p.187 (désignation subséquente de Desor., 1858, Synopsis des échinides fossiles, p.378 )

Extension stratigraphique (bibliographique, non vérifiée) : Eocène - Actuel

Syn.

• Kleinia Gray, 1851, p.133 ; Espèce type Kleinia luzonica Gray, 1851.

• Toxobrissus Desor, 1858, p.399 ; espèce type Brissopsis elegans Agassiz, 1847, p.184.

• Brissoma Pomel, 1883, p.41 ; espèce type Brissopsis duciei Wright, 1855, p.37.

• Bryssopsis Meissner, 1903, p.1343, nomen vanum.

• Toxobryssus Meissner, 1903, p.1395, nomen vanum.

• Zeugaster Lambert, 1907, p.106 ; espèce type Brissopsis lamberti Gauthier, 1900, p.42.

• Fernandezaster Sanchez Roig, 1952, p.18, espèce type Fernandezaster fernandezi Sanchez Roig, 1952.

Genus Brissopsis (Agassiz,1840).

     Form elongated, subcylindrical ; ambulacral areas straight, short, and wide, converging near the summit of the test ; peripetal fasiole flexuous, closely surrounding the ambulacral areas ; two or four genital pores, the posterior larger than the anterior pair ; five ocular plates disposed nearly equally apart in a

pentagonal form around the genital openings ; subanal fasciole wide, and situate at a considerable distance below the anal opening ; single ambulacrum lodged in an anteal sulcus ; the basal portions of the ambulacra are wide and naked ; the tubercles are very uniform in size, and are crenulated and perforated. Three living species ; the rest are fossil in the tertiary rocks.

CXXXXI. Genre. - BRISSOPSIS. Agass. 1847.

     Oursins renflés, ovoïdes. Sommet central ou excentrique en avant. Sillon impair peu accusé. Pétales inégaux, les antérieures droits et passablement divergents. Deux fascioles, l'un péripétale entourant les ambulacres, l'autres sous-anal formant un anneau placé à la base de la face postérieure.

     Des terrains tertiaires et de l'époque actuelle.

     Nota. Au point de vue des fascioles, ce genre est voisin des Brissus, et c'est ce qui lui a valu le nom de Brissopsis ; mais il en diffère notablement par son sommet ambulacraire médian, ses

pétales antérieurs bien moins divergents et par la présence d'un sillon antérieur. Le type de cette espèce est pour nous le B. lyrifera (Catal. rais. Tab. XVI. fig. 12). Parmi les espèces fossiles énumérées ci-dessous la plupart nous laissent des doutes sur la présence des fascioles. Ce n'est donc que sur la foi de leur aspect général et de la forme et de la position de leurs pétales que nous les citerons ici.

     Le genre Cyclaster Cotteau nous paraît coïncider de tous points avec le genre Brissopsis ainsi réduit.

Brissopsis crescenticus Wright,1854

Brissopsis crescenticus (Wright, n. sp.). Pl. VI. fig. 2 a-c.

     Test oblong, rounded before and truncated behind ; flattened on the dorsal surface, and deeply indented by the ambulacral areas ; the ambulacrum forms and anteal sulcus ; the anterior and posterior ambulacra on each side form two lateral crescents that abut at the longitudinal line ; the antero-lateral pair are the longest and widest, they curve fowards and backwards, and the posterior pair curve backwards and forwards ; the anterior pair form an angle of 45°, the posterior pair an angle of 65° ; the apical disc lies in a depression formed by the confluence of the apices of all the ambulacra ; the posterior border is squarely truncated, with the anal opening in its upper angle ; the base is convex, with few tubercles and wide naked spaces formed ty the basal portions of the ambulacra ; the mouth is situated in the anterior third.

     Dimensions. - Antero-posterior diameter 1  ^6/10 inch, transverse diameter 1 ^4/10 inch, height 8/10ths of an inch.

     Description. - The most remarkable feature in this species consists in the mode of arrangement of the ambulacra ; the anterorior and posterior areas of each side curve in opposite directions and form crescents, the convexities of which are directed towards the middle line of the test, and give value to the name proposed. The antero-lateral pair form an angle of 45° ; they are about the same length as the posterior pair, but are a little broader and are more divergent : there are nineteen pars of holes in the external zone, and fourteen in the inner ; the posterior pair are nearly parallel with each other, and have a slight curve forwards to form the posterior horm of the crescent ; they are not so much developed as the anterior pair ; the external zone of holes contains fifteen pairs, but the inner zone (2c) is imperfectly developed, from their close approximation to those of the opposite area : the apical disc is small ; the four genital holes are large, the anterior pair being more closely approximated than the posterior pair ; it is situated nearer the anterior than the posterior border and lies in a confluent depression, in which the apices of all the areas freely converge. The single ambulacrum is rather longer, but not so wide as the anterior pair ; its lateral row of single holes, with their accompanying tubercles, are small and indistinctly seen, and it froms and inconsiderable anteal sulcus : the posterior border is

squarely and obliquely truncated, and in its upper part near the dorsal surface is the large anal opening : the base is rather convex ; the sternal portion of the single interambulacrum is slightly  prominent, and ornamented with a few rows of rather larger tubercles disposed in zigzag lines : the basal tracks of the ambulacral areas are entirely naked, and where they ternate around the mouth five petaloid poriferous radii are observed. The mouth, of moderate size, is in the anterior third ; the peripetal fasciole is narrow and indistinct ; the subanal fasciole is much broader, and remote from the anus, but the test is unfortunately broken in this region ; the tubercles are nearly all of the same size, but a few larger ones occupy the sides, front, and base.

     Affinities and differences. - The flatness of the dorsal surface, the deep depressions made by the petaloid portion of the ambulacral areas, and the double crescent formed by them, readily distinguish B. crescenticus from its congeners. So few fossil species of this genus have been figured or described, that we can only compare it with the other forms obtained from the same bed, from both of which it differs in many well-marked characters.

     Locality and stratigraphical position. - It was collected from bed No. 4, the calcareous sandstone at Malta, where it is rare.

Planche VI (extrait)

Brissopsis crescenticus Wright,1854 - Lower Globigerina limestone, Gozo, Malte, 35 mm

Brissopsis mediterranea Mortensen, 1913

Brissopsis mediterranea Mortensen, 1913 - Miocène, Sesimbra, Portugal, 29 mm