166 THE CHICAGO ACADEMY OF SCIENCES. 



Shell: Subglobose, solid, umbilicate or imperforate; sur 

 face covered with very fine, oblique growth lines which are so 

 minute as to be scarcely visible even when viewed with a pow- 

 erful glass; the surface is also set with short hairs scattered 

 over the whorls; nuclear whorls smooth; periphery rounded; 

 sutures well impressed; color yellowish to reddish horn; 

 whorls five to five and one-half closely coiled, flatly rounded, 

 the last gibbous on the last half and constricted behind the 

 peristome; spire somewhat elevated in some specimens, but flat 

 in others, convex; aperture narrowly lunate, no teeth or notches 

 on the peristome; parietal wall with a long, narrow, more or less 

 elevated tooth, which begins near the center of the parietal wall 

 and extends generally to the umbilical region in a line parallel 

 with the basal reflection of the peristome; peristome white, 

 thick, reflected, umbilicus widely open, or wholly imperforate; 



FIG. 26. 

 Jaw of POLYGYRA MONODON Rackett. (Original.) 



the region strongly depressed; base of shell rounded, with a 



transverse internal tubercle. 



Greater diameter, 8.50; lesser, 8.00; height, 4.50 mill. (8454.) 

 9.00; " 8.25; " 5.25 " (8453.) 

 8.50; " 7.75; " 5.00 " (9128.) 



Animal: With a long, narrow foot truncated before, pointed 

 behind; head distinct; tentacles short, cylindrical, thick; eye- 

 peduncles long, thick, not much tapering, the black eyes situ- 

 ated on large swellings at the tips; color brownish-yellow, al- 

 most black on head, neck, tentacles, and eye-peduncles, lighter 

 on the foot; respiratory orifice not large. Heart situated be- 

 tween the tooth on the parietal wall and the junction of the 

 upper part of the peristome with the body-wall. Pulsations 

 regular, seventy-one to seventy-six per minute. Length of 

 foot II, width 2 mill. 



Jaw: Arched, ends blunt, rounded; anterior surface with 

 seven stout ribs which denticulate both margins (Fig. 26). 



Radula formula: f+Y+ V + i + V + Y+f (24-1 -24); 



