Notes on Radulce. 



85 



Helisoma trivolvis Say. Plate IV, K. 



Radida formula + J + \ + J + §^ (1 9-1- 19) ; central 

 tooth with a base of attachment longer than wide, swollen 

 and rounded on the lower half, reflexion broad, bicuspid, the 

 cusps long and narrow, fang-like; lateral teeth with a quad- 

 rate base of attachment and a large, square reflexion which 

 is tricuspid, the center cusp being very wide and blunt and 

 the side cusps long and narrow and directed outward; inter- 

 mediate teeth similar to laterals, but varying in the number 

 and arrangement of the cusps; sometimes the change from 

 laterals to marginals is abrupt, at others it is very gradual, 

 and in some membranes there appear to be no two marginals 

 alike; the large, blunt central cusp in the lateral teeth be- 

 comes a long and narrow cusp in the intermediate (transition) 

 teeth and the side cusps become much larger, so that all three 

 cusps are about equal; in addition to this, the outer edge of 

 the outer cusp develops several small denticles; marginal 

 teeth long and narrow, with three small cusps at the distal 

 end and several (3-4) small denticles on the outer edge. A 

 number of specimens have been examined. 



Helisoma truncatus Say. 



But a single specimen of this species has been examined 

 and did not seem to differ from H. trivolvis. The formula was 

 + * + * + * + if (22-1-22). The specimen 

 examined was a large example, characterized by the lattice- 

 like sculpture peculiar to this species. 



Helisoma bicarinatus Say. Plate IV, F. 



Radula formula §f + f + f + i + f + ff (30 - 1 - 30); cen- 

 tral tooth as usual ; lateral teeth of usual shape, but reflex- 

 ion with a large squarish central cusp, a large rounded inner 

 cusp and a smaller outer cusp; transition teeth (9) with three 

 nearly equal, rather sharp cusps; marginal teeth, as in tri- 

 volvis. The writer counted 136 rows of teeth. 



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