NEW FKKSll WATEIt ANO LAM) SHELLS. 39 



the posterior slope ; epidermis dull, dark olive and without rays ; umbonial slope 

 angular ; posterior slope very broad and flattened, with two obscure impressed lines ; 

 anterior slope widely cordate and flattened, with a large, slightly impressed furrow ; 

 anterior lunule broad with several transverse, impressed parallel lines ; cardinal teeth 

 crenulate, compressed, transverse, short, the upper division longer, double in each 

 valve ; the two anterior inferior cicatrices deeply impressed and confluent, the superior 

 one placed on the inner side of the tooth ; posterior cicatrices confluent ; dorsal 

 cicatrices placed within the cavity of the beaks, and but partly visible ; pallial cicatrix 

 very slightly impressed; cavity of the shell very deep and rounded; cavity of the 

 beak very deep and subangular; nacre white and very iridescent. 



Remarks. — I procured this very remarkable shell in Paris, from Mr. E. Verreaux, 

 whose researches and collections in South America, Africa, &c., have been so extensive. 

 It has the general aspect of a very much inflated Monocondylmi Paragiuiyana, D'Orb., 

 but the form of the teeth is totally different, and the shell thinner and more vesicular. 

 The anterior slope is almost as cordate as Isocardia Moltldana, Lam., the beaks 

 presenting an incurved form somewhat like that shell. The angle on the umbonial 

 slope is also somewhat similar and it has a like flattened side. The anterior lunule 

 is very wide, and immediately under the point of the beaks there are three transverse 

 impressed lines, very unusual in the Ndiadefi, which may not be constant even in this 

 species. 



Triquetra contorta. pi. 33, fig. 33. 



Testa nodulosa, transversissima, subcompressa, tortuosa, valde insequilaterali, postice acuto-angulatfi ; antic6 

 caudatim producta ; valvulis crassis ; natibus parvis, prominulis, ad quartam anteriorem partem positis ; 

 epidermide striata, tenebroso-fusca ; dentibus cardinalibus subgrandibus, crenulatis, in utroque valvule 

 duplicibus ; lateralibus proslongis curvisquc; margarita argcntea et iridescente. 

 Shell verrucose, exceedingly transverse, rather compressed, twisted, very inequi- 

 lateral, acutely angular behind ; anterior margin lengthened into a tail; valves thick ; 

 beaks small, slightly prominent and placed one-fourth from the anterior margin ; 

 epidermis striate, dark brown ; cardinal teeth rather large, crenulate and double in 

 both valves ; lateral teeth exceedingly long and curved ; nacre silvery white and 



iridescent. 



Triquetra lanceolata, Lea. Proc. Acad. Nat. Sci. Vol. 8, p. 79. 



Hah. — China. Mr. Asa Fitch and H. Cuming, Esq. 



My cabinet and cabinet of H. Cuming, Esq., London. 

 Diam. -9. Length 1-3. Breadth oS inches. 



Shell warty, exceedingly transverse, rather compressed, twisted, very inequilateral, 

 acutely angular behind ; anterior margin lengthened into a tail-shaped prolongation ; 

 substance of the shell thick ; beaks small, slightly prominent and placed one-fourth 

 of the whole breadth from the nntorinr margin ; epidermis striate, dark brown and 



