116 THE CHICAGO ACADEMY OF SCIENCES. 
Remarks: This isa common and widely diffused species, 
occurring in all parts of the area under discussion. Particularly 
large and fine specimens are found in the DuPage River near 
Lisle. Some little variation exists, principally in the relative 
length and height. It may easily be recognized by its inequi- 
lateral form and very heavily marked umbones. 
On July 25, 1896, the writer found young in the inner gills, 
measuring from two to five or six millimeters in length, three 
or four being found in each gill. The animal is quite active, 
moving by a series of jerks. Progression is effected by means 
of the foot, which is thrust out to its fullest extent and the shell 
drawn after it. It is very interesting to watch this species in an 
aquarium and notice its quick, jerky motions. It thrives well 
in captivity, and is very well adapted for anatomical investiga- 
tions, owing to its large size. 
39. Sphzrium simile Say, pl. xxvii., fig. 3. 
Cyclas similis Say, Nich. Encyc., Am. Ed., Vol.-II., pl. i., fig. 9, 1817. 
Cyclas sudcata LAMARCK, An. sans Vert., Vol. V., p. 560, 1818. 
Cyclas Sarratogea LAMARCK, I. c., p. 560, 1818. 
Cyclas lasmampsis RAFINESQUE, An. Gen. Sci. Phys. et Nat., Vol.V., p. 319, 
pl. Ixxxii., figs. 19, 20, 1820. 
Cyclas solida DeKay, Moll. of N. Y., p. 229, pl. xxv., fig. 265, 1843. 
Cyclas gigantea PRIME, Proc. Bost. Soc. N. H., Vol. IV., p. 157, 1851. 
Cyclas ponderosa PRIME, |. c., p. 157, 1851. 
Shell: Warge, inflated, rather solid, almost equilateral, 
transversely oval; umbones depressed, inflated, placed a trifle 
anterior to the center of the shell, marked by heavy ridges, but 
not so coarse as in stamineum; dorsal margin very nearly 
straight, ventral border broadly curved; anterior and posterior 
margins almost equal, the posterior a little longer than the an- 
terior, the two margins rounded; umbonal slopes rounded; sur- 
face shining, growth lines coarse; color dark brown, sometimes 
with a reddish tinge; ligament weak, very dark horn or black; 
cardinal teeth small, a single, long, stout, elevated, arched tooth 
in the right valve, and two stout, elevated teeth in the left valve, 
the upper tooth being short and curved and the lower tooth 
long and almost straight; one specimen (10882) seems to have 
the teeth in the right valve double and placed like those of the 
left valve; the teeth are sometimes very long and lamellar 
(8513); lateral teeth double in the right and single in the left 
valve, short, elevated, lamellar, nearly straight; muscle scars 
