198 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [NoT. 21, 



BrISSUS (HeMIASTEr) SXJBDEPRESSUS, Sp. UOY. Pl. XXY. fig. 6. 



B. (H.) testa subcordata, superne depressa, area anali elevata, cariuata, lateribus 

 tumidis, postice truncata; ambulacris lateralibus latis subcEqualibus, impressis, 

 area post-orali lanceolata. 



Length ^ incli ; breadtti ^ inch ; height -^ inch. 



This little species is alhed to the Spatangv.s Bufo of authors, and 

 to the Micraster minimus of Agassiz, but differs from them and from 

 most of its described congeners in the depression of its back, Ts'hich 

 has only a rery shght and gradual slope from the elevated posterior 

 interambulacral area. The ambulacra are rather broad, and seated 

 in not veiy deep depressions with rounded sides. Each linear series 

 of double pores in the antero-lateral ambulacra of the largest speci- 

 men examined consists of twenty-seven pair, and in the postero-late- 

 rals of twenty-four. The sides and under surface were rough with 

 spinigerous tubercles. The mouth is placed not veiy far forward, 

 and the spinous space behind it is lanceolate in shape. The anal ex- 

 tremity is suddenly truncated, but with a slight obliquity. Young 

 specimens are much more depressed than old ones. 



It is not unlikely that this may be one of the numerous species of 

 Hemiaster enumerated by Desor in the ' Catalogue Raisonne des 

 Echinides'j but ^vithout figures or descriptions to guide us, it is im- 

 possible to recognize mere names with localities only appended, or 

 notices so brief as to be useless. 



This Brissns occurs in the subcretaceous hmestone of Figueira 

 and is apparently plentiful. Its afiinities are with cretaceous species, 

 especially those of the Gault. 



Along with it a form is fomid with longer and narrower ambidacra 

 and greater tumidity of the sides. This is possibly distinct, but the 

 specimens examined are too fragmentary for determmation. It occurs 

 also at IMamarosa. 



Plate XXY. fig. Q a & b. Usual form. 



Fig. 6 c. Yariety. 



BRissrs scutiger. Pl.-XXY. fig. 5. 



B. (Brissopsis) testa cordata, tumida, superne subdepressa, area anali couvexa, 

 declivente, lateribus prominentibus, postice rotundato-truncata, ambulacris 

 antero-lateribus lanceolatis impressis, postero-lateralibus ovatis-oblongis, area 

 post-orali triangulari. 



Breadth 1^ inch ; length l^ inch ; height -^ inch. 



The outhne of this Brissus is cordate, truncate posteriorly, tumid 

 at the sides. The true apex is nearly central, and from that point 

 the back declines gradually in front and rises suddenly posteriorly, 

 but the rise is very brief, and then there is a gradual gently curved 

 declension to the oval, not very large anus. The hinder extremity is 

 truncated steeply with a slight obhquity. The ambulacra are placed 

 in gentle, but conspicuous depressions, all equally deep. The antero- 

 lateral ones T\idely diverge, the postero-laterals but slightly compara- 

 tively. In the former there are about thhty pairs of pores in each 

 row, in the latter about twentv-four. The former are broadlv lanceo- 



