29 



than shelly) resembles that of Anomia, does not perforate the lower 

 valve directly, but is inserted between the laminae of the internal 

 surface of the lower valve above the muscular impression and below 

 the hinge, and passes out into an external irregular somewhat lon- 

 gitudinal superficial fissure or cicatrix, which is narrowest at the 

 hinge margin, and which it entirely fills to a level with the sur- 

 rounding surface of the shell. 



Placunanomia Cumingii. Plac. testa subrotundatd, obscure 

 argenteo-albidd, complanatd ; margine plicato, plicis maximis : 

 long. 2-^, lat. tV, alt. 2% poll. 

 Hab. ad oras Americae Centralis. (Gulf of Dulce, Province of 



Costa Rico.) 

 Dredged from a muddy bottom, at a depth of eleven fathoms, 

 attached to dead bivalve shells and dead coral. — W. J. B. 

 Genus Dentalium. 

 Dentalium splendidum. Dent, testa tenui, politd, basi earned, 

 apice majori lacted ; aperturd posticd Jissuris duabus, alter d dor- 

 sali, alter d ventrali : long. 1^V> lot, -^V poll. 

 Hab. ad oras Americae Meridionalis. (Xipixapi, West Columbia.) 

 Dredged in from ten to sixteen fathoms water, on a sandy muddy 



bottom G. B. S. 



Dentalium tesseragonum. Dent, testa tenui, lacted, Icevi, 



primum tetragond, ob angulos evanescentes dein cylindricd; linen 



incrementi tenuissimis annulos subhyalinos effbrmantibus : long. 



tV, lat. -rV poll. 



Hab. ad oras America? Centralis. (Gulf of Nocoiyo and Puerto 



Portrero -, also Xipixapi.) 

 Var. angulis indistinctis • lineis incrementi annulos efFormantibus. 

 Obtained in the same manner as the preceding species. — G. B. S. 

 Dentalium quadrangulare. Dent, testa parvuld, albd, qua- 

 drangulari, angulis acutiusculis, interstitiis striatis ; aperturd 

 tetragond: long. -^, lat. y ff poll. 

 Hab. ad oras Americae Meridionalis. (Xipixapi.) 

 The colour of this shell is variable, being either milk-white, yel- 

 lowish, or reddish ; the angles are less acute at the larger end; and 

 at the smaller end there is sometimes formed a tubular appendage. 

 — G. B. S. 



Dentalium perpusillum. Dent, testa minima, tenui, angusta, 

 curvd, politd, albd ; apice acuto ; aperturd coarctatd, obliqud : 

 long. -rV, lat. -jV poll. 

 Hab. ad oras Americas Meridionalis. (Puerto Salango, West Co- 

 lumbia.) 

 This is related to Dent. Gadus, but is much more slender, and 

 the aperture is obliquely truncated from the dorsal to the ventral 

 margin. — G. B. S. 



Genus Helix. 

 Helix Monile. Hel. testa globosd, turgido -plana, translucidd, 

 corned, superne maculis strigisque angulatis moniliformibus or- 

 natd; spird excavatd ; umbilico magno : long. T \, kit. 1 poll. 



