THE NATURAL HISTORY SURVEY. . 207 



short, cylindrical; foot grayish white in color, truncate before, 

 bluntly rounded and flattened behind; a lateral groove runs 

 from the head to the posterior part, just at the edge of the foot, 

 and meets in an acute angle behind; respiratory orifice on right 

 side, just beneath the peristome of the shell and near its junc- 

 tion with the body-whorl; mantle colored like shell. Length 

 of foot 26.00 mill., width 6.00 mill. 



The heart is situated 3 mill, from the junction of the per- 

 istome with the body wall, and the pulsations are very regu- 

 lar. Fifteen experiments gave the following number of pulsa- 

 tions per minute: 84, 82 (twelve specimens), 61, 50. The last 

 two figures were taken when the animal was contracted, and 

 the heart-beats much slower. 



Jaw: Arched, broad, ends broadly rounded; concave mar- 



FIG. 48. 



Radula of PYRAMIDULA ALTERNATA Say. (From nature, after Pils- 

 bry, Guide to Helices, pi. xi, figs. 18,23.) C, central tooth; 1, first lateral; 

 11, first marginal; 27, sixteenth marginal; J, jaw. 



gin not very much crenulated, with a rounded median projec- 

 tion; anterior surface marked by vertical striae (Fig. 48, J). 



Radula f orm ula : ^t+ J^+i+ + (34 - I - 34) J central 

 tooth with a subquadrate base of attachment, somewhat ex- 

 panded on the lower outer corners; reflected portion with one 

 long central cusp reaching below the lower edge of the base 

 of attachment, and two very small side cusps with small cut- 

 ting points; lateral teeth (ten perfect) longer than wide, bicus- 

 pid, the inner cusp long and narrow with a long, narrow cutting 

 point, and the outer cusp short and wide with a short cutting 

 point; marginals variable, at first like the laterals, but becoming 

 wider toward the margin (twenty-seven) and with one long inner 

 cusp and a short outer cusp. The cutting point is generally 

 one-third the length of the cusp (Fig. 48). There are about 120 

 rows of teeth. 



