THE NATURAL HISTORY SURVEY. 173 



especially if it be moistened. The pulsations are very regular, 

 but vary in number, being more numerous when the animal is 

 extended, as during locomotion, and few when the animal is 

 contracted. From twenty experiments the following data are 

 taken, ranging from the smallest to the highest number: 50, 

 56, 72, 75, 78, 82. Temperature greatly affects the heart, cold 

 causing it to apparently cease, while heat accelerates its action. 



Jaw: Crescent-shaped, with bluntly rounded ends; con- 

 cave margin smooth, supporting a median projection; striated 

 on its anterior face (Fig. 30, B). 



Radula formula: V+f+^+f+V (25 I 25) in 32 rows; 

 central tooth small, triangular, with a rather large base of at- 

 tachment which is much expanded on the outer lower corners; 

 the apex of the triangle is truncated and incurved, the cut- 



FIG. 30. 



A, teeth, and B, jaw of CIRCINARIA CONCAVA Say. (Original.) c, 

 central tooth; 1, first lateral; 6, sixth lateral. 19, thirteenth marginal; 24, 

 nineteenth marginal. 



ting point long and well-developed, with subobsolete side 

 cusps; lateral teeth with as ole-shaped base of attachment, the 

 lower lateral expansions angular; cusps long and slender, cut- 

 ting points long and narrow, with subobsolete side points; 

 marginals (all after the first six) long and aculeate, base of 

 attachment sole-like with long and narrow cusps and cutting 

 points (Fig. 30, A). Binney gives 20-1-20 and 23-1-23 teeth. 



Distribution: Maine west to Minnesota and Iowa, Canada 

 south to Georgia and Mississippi. 



Geological distribution: Pleistocene; Loess. 



Habitat: Found buried in the soil under dead and decaying 

 logs, fallen underbrush and rubbish. It prefers a forest that is 



