152 THE CHICAGO ACADEMY OF SCIENCES. 



Shell: Depressed globose, rather solid, imperforate; sur- 

 face covered with numerous fine, oblique striae which are obso- 

 lete on the apical whorls, and the whorls are encircled by very 

 numerous fine, wavy, spiral lines, which give the surface a lat- 

 ticed aspect under the glass; color yellowish-brown, sometimes 

 darker, without bands; periphery rounded; sutures much im- 

 pressed; whorls five to six, rounded, regularly increasing; spire 

 but little elevated; aperture lunate, contracted by the peristome; 

 peristome widely reflected, white, flattened, with sometimes a 

 small callosity near the columella, which is nearly straight; 

 umbilicus covered in the adult shell by the reflection of the 

 peristome, which forms a spreading callus; base of shell convex. 



Greater diameter, 32.00; lesser, 26.00; height, 19.00 mill. (7972.) 

 30.00; " 24.50; " 18.00 " (8091.) 



Animal: With a long foot which is wide and spreading at 

 the base, and slopes up to meet the rounded body and neck; 

 posterior extremity of foot flattened and spreading, acutely 

 pointed, and rising to meet a central dorsal keel. Color yel- 

 lowish-brown, with a dark stripe extending down the center of 

 the neck and head to the shell; tentacles and eye-peduncles 

 almost black; sometimes darker along sides of body; the 

 animal is sometimes whitish or cream-colored, and may be 

 almost black. Eye-peduncles very long, bearing the black 

 eyes; tentacles short and cylindrical, tubercles on the back very 

 prominent and arranged longitudinally. The foot of a large 

 specimen measured 60 mill, in length and 14 mill, in width, and 

 the eye-peduncles measured 13 mill, in length. The heart 

 pulsations areas follows: 50-56-61 (adult); 69 (half-grown); 

 106 (very young); 48 (animal dormant). 



Radula formula : y + V + +1+ + + V ( 44 - 1 - 44 ) 

 (sometimes 45 145). Central tooth with a long and narrow 

 base of attachment, the lower outer corners expanded and the 

 base excavated; reflection reaching below the margin of the 

 base of attachment, with the cusps similar to those of tridentata, 

 but narrower; lateral teeth similar to central; marginal teeth 

 at first like lateral teeth, but soon (28) the inner cusp becomes 

 bifid, the cusp becomes wider (30 35) and extends far below 

 the base of attachment. Thirty-eight is a marginal of abnormal 

 form; one row had all of the thirty-eighth teeth of this form 

 {Fig. 20). There are over 120 rows of teeth. 



Jaw : Similar to that of thyroides, but very arcuate and with 



