GENERA AND GROUPS OIP THE ECHINOIDEA. 241 



Peristome excentric in front, transversely elliptical, witli a 

 small posterior projecting labrum. 



Ornamentatiou o£ very small raised perforate and crenulate 

 tubercles abactinally, vyith numerous small granules which are 

 very marked in tbe anterior groove ; tubercles larger, sunken 

 and surrounded by granules actiually, and crovfded in lines on 

 the post-oral region. 



Fossil. Cretaceous : England, Europe, Africa, S. Hindostan. 

 Eocene: Asia (Sind). Miocene: Australia. 



Loven has pointed ou.t that the episternum is not developed 

 in this geniis, which is nevertheless amphisternous, the arrange- 

 ment foreshadowing that of the later Spatangoids. The forms 

 included in the genus have an Ethmophract apical system, the 

 fifth basal plate being absent, and the madreporite sometimes 

 slightly separates the postero-lateral basals. There are some 

 plates of the bivium between the petaloid part and the subanal 

 fasciole which are uniporous ; but all the plates of the trivium 

 are biporous. The petaloid arrangement is rather imperfect, the 

 distal ends not absolutely closiug ; usually the grooves between 

 the plates of the ambulacra, except the anterior, are very distinct. 



Subgenus Brissopneustbs, Cotteau, 1886 (genus), Bull. Soc. 

 Zool. de France, vol. xi. p. 712, pi. xxiii. figs. 9-12. 



Test small, oval, ovoid, elongate, narrowest and truncated poste- 

 riorly, tumid dorsally aud slightly actinally. 



Apical system excentric in front, small ; four basal plates in 

 contact and three are perforated. The madreporite in the right 

 anterior imperforate basal plate. The anterior poriferous zone 

 of the antero-lateral ambulacra smaller than the posterior zone. 



Fossil. Eocene: Europe. 



In dealing with the affinities of this somewhat doubtful genus, 

 M. Cotteau compared it with Isopneustes, Pomel, 1883, Theses, 

 p. 43, a genus (?) which was defined in relation to Micraster, and 

 has " pas de fasciole peripetale, ni probablement de sous-anal." 



M. Seunes, 1888, Bull. Soc. Geol. de France, vol. xvi. p. 793, 

 states that there is a partial peripetalous fasciole in Isopneustes, 

 and hence the genus has not been sufficiently diagnosed. 



G-enus Beissus, Klein, 1734, Nat. Disp. FcJi. p. 36. Gray, 1825, 

 Ann. Phil. p. 9. Agassiz Sf Besor, 1847, Cat. Bais., Ann. d. 



LINN. JOUEN. — ZOOLOGY, VOL. XXIII. 16 



