42 



CONCHOLOGY. 



thick, smooth, or without tentacular papillae, augmented behind 

 by two indistinct tubes ; mouth small and oval ; labial appendages 

 narrow ; branchial laminae very small, and united in their length 

 among themselves and with those of !he opposite side ; foot oval, 

 trenchant, very long. 



Shell. The Mactra has a peculiar hinge distinguishing it from 

 all other genera. It is triangular, with a curved or angular com- 

 pressed tooth on each valve, with a small oblique cavity on each 

 side, to which is attached the ligament. Two lateral teeth, one 

 near the primary tooth and one near the ligament. The shape 

 of the shell is subtriangular or oblong; exterior smooth, striated, 

 or ribbed transversely ; two muscular impressions united by a 

 narrow marginal tongue. Inhabits the British and American 

 coasts. Forty -four species. 



Mactra spengleri. 

 M, striatella. 

 M. carinata. 

 M. straminea. 

 M. Australis. 

 M. violacea. 

 M. fasciata. 

 M. turgida. 

 M. plicataria 

 M. rufescens. 

 M. maculata. 

 M. subplicata. 

 M. triangularis. 

 M. lactea. 

 M. abbreviata. 

 M. crassatella. 



Mactra helvacea. 

 M. grandis. 

 M. stultorum. 

 M. maculosa. 

 M. ovalina. 

 M. castanea. 

 JVI. rufa. 

 M. squalida. 

 M. Brasiliana. 

 M. donacintu 

 M. depressa. 

 M. lilacea. 

 M. trigonella. 

 M. deitoides. 

 M. alata. 



M. gigantea.* 

 M. solida.* 

 M. oblonga.* 

 M. californica.* 

 M. arctata.* 

 M. nucleus.* 



M. alba.* 

 M. similis.* 

 M. fragilis.* 

 M. lateralis.* 

 M. dcaurata.* 

 M. planulata.* 



M. tellinoides.* 



