12 



AMERICAN CORBICrLAD^. 



made to include several genera which have since been diverted 

 ffoni it — Corhicula, Batiasa and VeJorita. The genus, as now 

 most generally received, embraces only the species of Cyrena witli 

 simple lateral teeth. 



Cyrena in a living state are found in all tropical countries. 

 The genus is represented at the present time in North America but 

 by one species ; in Central and in South America the species are 

 numerous and bountifully distributed. I am not aware that, out- 

 side of America, any of the so-called Marine Cyrena have been 

 found. A peculiarity of the Cyrena of this continent lies in the 

 fact that the palleal impression is always terminated in a sinus, 

 whereas in those from other parts of the world it is simple. 



C. caroliniensis. 



a. Cyken^ proper. 



1. Cyrena carolillieiisis, Lamarck. — Shell orbicular-trigonal, 



inequilateral ; margins generally round- 

 ed ; beaks obtuse, oblique, often eroded ; 

 striae very fine ; epidermis rough, of a 

 grayish olive-green ; valves moderately 

 full, not heavy ; interior white in adult, 

 pale bluish in young, occasionally with 

 markings of light violet on the margins 

 and on tlie hinge ; hinge-margin nar- 

 row ; cardinal teetli small ; lateral teeth 

 short, obtuse ; sinus very narrow, acute 

 at extremity. 



Long. 1.44; Lat. 1.16; Diam. .94 inch. 

 " 38; " 33; " 25 mill. 



Hab. North America, in the States of Alabama and Georgia. (Cabinets 

 of the British Muse^im, Smithsonian Institution, Cuming, Jay, Prime and 

 others.) 



Ci/rlas caroliniensis, Bosc, Fer. Cat. Meth. 1807. 



Ci/clas caroliniana, Bosc, III, 37, pi. xxiii, f. 4. 



Cijrena caroliniensis, Lam. An. s. vert. V, 1818, 558. — Say, pi. 52. 



This, our most common species of Cyrena, is not very liable to 

 be confounded with any other ; in exterior it bears some resem- 

 blance to C. mexicana, it differs, however, in being larger, 

 more trigonal, the beaks are less prominent and the sinus is nar- 

 rower and more acute. The young shell is less elongated trans- 

 versely and more quadrangular than the adult. 



