FAMILY CYCLAD^I — CYCLAS. 225 



This species occurs along the borders of Lake Champlain, where it was first noticed by- 

 Mr. Adams. It appears to be closely allied to what I consider to be the C. rhomboidea of 

 Say, but differs chiefly in .the cardinal teeth, which in this species are very slightly developed. 



Cyclas edentula. 



Cyclas edentula. Say, Desc. fluv. and terr. shells, p. 10. 



Description. Shell transversely oval, inequilateral, with somewhat elevated and regular 

 transverse lines. Beaks not elevated above the general surface. Cardinal tooth very small, 

 lineolar, oblique, and not elevated higher than the edge of the hinge-margin : umbones de- 

 corticated. Color, brown. 



Length, 0-35; breadth, 0-4. 



This species, which I only know through the very brief notice of Mr. Say, was observed 

 by him in the Canandaigua lake in this State. It is distinguishable, according to Say, by the 

 diminutive teeth, which are not visible in a profile view of the hinge. The only species I 

 could find in that lake was the C. similis, with the young of which this may possibly have 

 been confounded. 



(EXTRA-LIMITAL.) 



C. transversa. (Say, Op. sup. cit.) Transversely oblong, subovate, subinequilateral : anterior margin 

 decidedly more widely rounded than the posterior margin ; beak obviously elevated above the gene- 

 ral curvature ; cardinal teeth double, distinct. Length, O - 25; breadth, 0-45. Kentucky. 

 .C. staminea. (Conrad, Am. Jour. Vol. 25, p. 342.) Shell oval, regularly convex, inequilateral: 

 anterior and posterior ends similarly rounded ; umbo inflated; beaks slightly prominent; apex 

 obtusely rounded ; lateral teeth rather prominent ; cavity rather capacious. Color : epidermis yel- 

 lowish, with darker stains; within bluish white. 



C. elevata. (Hald. Proceed. Ac. Sc. 1841.) Shell orbicular: cardinal tooth prominent; lamellar 

 tooth thick ; beaks elevated. Color, brownish olive. Length, 0-55; height, 0-5. New-Orleans. 



Genus Pisidium, Pfeiffer. Shell equivalve, transverse; sides unequal, completely closing. In the 

 right valve one, in left valve two, opposite very small primary teeth : behind and before, two 

 thin lamellar side-teeth ; those of the latter cleft in the right valve, in order to receive the op- 

 posite ones. Animal with a narrow fleshy projection next the forepart of the shell, instead 

 of a tubular trachea : foot long and thin. 



Obs. This genus was separated from Cyclas by Mr. Pfeiffer ; but conchologists have not 

 agreed as to the propriety of its creation. Deshayes observes, that the author " s'apercut, en 

 etudiant les animaux des cyclades, qu'il y en avait une dont les siphons posterieurs sont beaucoup 

 plus courts que dans les autres especes, et depassent a peine les bords de la coquille. II crut 

 ce caractere suffisant pour justifier la creation d'un genre sous le nom de Pisidium. Nous ne 

 croyons pas qu'il soit utile d'adopter ce genre, ses caracteres ayant trop peu de valeur." 

 Fauna — Part 6. 29 



