216 



has fewer angularities than any other Mactra. It is also peculiar 

 for its very wide gape. 



Mactra cuneola. T. parva, crassiuscula, rudis, ovato-cune- 

 ata, albida, epidermide stramineo induta, concentrice striata ; 

 umbonibus submedianis, tumidis, acutis, anteversis ; latere 

 antico angustato, subacuto ; latere siphonali breviori, tumidiori, 

 sublruncato : area cardinalis minima ; fovea ligamentali indis- 

 tincta ; dente V-formi conspicuo ; dentibus lateralibus curtis, 

 elevatis ; sinu siphonali minimo, quadrantem testse solum tran- 

 seunte. Long, f ; alt. ^ ; lat. -^^ poll. Hab. Callao. 



In most of its characters it corresponds with our M. lateralis ; 

 but in this shell it is the posterior end which is shortest and 

 broadest, while the reverse is the case in that species. 



Mactra marcida. T. ventricosa, ovato-triangularis, cretacea, 

 epidermide tenui stramineo induta ; umbonibus medianis, tumi- 

 dis, remotis, vix anteversis ; latere antico breviori, rotundato ; 

 latere siphonali subtriangulato, acuto ; margine ventrali arcuato : 

 fovea ligamentalis ampla, dente V-formi parvo, prominente ; 

 dentibus lateralibus crassis, parum elevatis : interior cretacea ; 

 sinu siphonali parvo, trientem testes attingente. Long. 2f ; 

 alt. 2|-; lat. 1|- poll. Hah. Orange Harbor. 



This species has pi'ecisely the form of M. lactea, but is a 

 much more solid and rude shell, wanting also the decided dorsal 

 angularities of the umbones. 



Mactra falcata. Testa magna, transversa, ovato-trigona, 

 inequilateralis, convexiuscula, modice hians, albida, epidermide 

 fulvo, nitido, concentrice rugoso induta ; umbonibus acutis, 

 approximatis ; latere antico acuminate ; latere siphonali late 

 rotundato, sub-truncato ; margine dorsali recto; area dorsali 

 planulata, lanceolata ; margine ventrali leniter arcuato : area 

 cardinalis ampla ; fossa ligamentali magna, dente V-formi parvo, 

 crasso ; dentibus lateralibus compressis, quorum antico valvse 

 dextrse bilobato : interior lactea ; sinu siphonali angusto, elon- 

 gate, spatulato. Long. 3J; alt. 2|- ; lat. 1^ poll. Hah. Puget 

 Sound, Oregon. 



This fine species compares best with M. Brasiliana and M. 

 ovalis. Its external form corresponds closely with the former, 

 while the narrow siphonal sinus and the hinge closely resemble 

 the latter. The bilobed lateral tooth is quite peculiar. 



