FAMILY CYCLADA— 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. s¢milis, 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, 0-25; breadth, 0-45. Kentucky. 
C. staminea. (Conrap, 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. (Hap. Proceed. Ac. Sc. 1841.) Shell orbicular: cardinal tooth prominent; lamellar 
tooth thick; beaks elevated. Color, brownish olive. Length, 0°55; height, 05. New-Orleans. 
Genus Pistprum, 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 oncs. Animal with a narrow fleshy projection next the forepart of the shell,” instead 
of a tubular trachea: foot long and thin. 
Oss. 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 
étudiant les animaux des cyclades, qu’il y en avait une dont les siphons postérieurs sont beaucoup 
plus courts que dans les autres espéces, et dépassent 4 peine les bords de la coquille. Il crut 
ce caractére suffisant pour justifier la création d’un genre sous lenom de Pisidium. Nous ne 
croyons pas qu’il soit utile d’adopter ce genre, ses caractéres ayant trop peu de valeur.” 
Fauna — Parr 6. 29 
