284 THE CHICAGO ACADEMY OF SCIENCES. 



Animal: Dark horn-colored, tinged with bluish on the 

 foot; head. distinct, separated from the body by a constriction 

 or neck, and produced into lateral flaps or vela; tentacles tri- 

 angular, rather long, flat, the eyes placed on their bases; foot 

 short and wide, truncated before and roundly pointed behind, 

 20.00 mill, long and Q.OO mill, wide; respiratory orifice very 

 large, placed near the junction of the peristome with the body 



FIG. 92. 

 Animal of LIMN^EA STAGNALIS Linn6. (Canadian Naturalist.Vol. II, p. 196.) 



whorl. Heart situated midway between upper and lower ends 

 of columella, pulsations varying from thirty-seven to forty- 

 eight per minute (Fig. 92). 



Jaw: As usual. 



Radula formula: 9 +A++ i. + . +A+f 9 (46-1-46); 

 central tooth as usual, a single membrane examined had the cen- 

 tral tooth abnormal in possessing a denticle on the left side of 

 the reflection (Fig. 93, c.); lateral teeth with a quadrate base 

 of attachment, the reflection very large, reaching far below the 

 base of attachment, bicuspid, the inner cusp very large, the 

 outer cusp very small (the first lateral has a bifid inner cusp); 

 intermediate teeth very long and narrow, bi- or tricuspid; mar- 

 ginal teeth very long and narrow, four or more cuspid, the cusps 

 being very blunt and small and extending irregularly along 

 the outer edge of the teeth. The number of teeth seems to 

 vary in different individuals: the writer has counted from 46- 

 1-46 to 54-1-54; Binney (L. and F. W. Sh., p. 28) gives 40-1-40 

 and (p. 155) 47-1-47 teeth; Bland and Binney (Am. Journ. 

 Conch., Vol. VII., p. 161) give 40-1-40. It is probable that 

 the membrane having 54-1-54 teeth was abnormal. 46-1-46 

 is the number generally counted by the writer (Fig. 93). 



Genitalia: Not examined. 



Distribution: North America, from the Atlantic to the 

 Pacific Oceans. 



