THE NATURAL HISTORY SURVEY. 145 



rounded; sutures impressed; whorls, five and one-half, convex, 

 closely coiled, the last deflected above the aperture and con- 

 stricted behind the peristome; spire depressed, a little convex; 

 aperture lunate, lobed by the teeth on the peristome; the tooth 

 on the upper part of the outer lip is broad and low, placed 

 squarely on the peripheral portion of the lip; the one on the 

 basal portion of the lip is small and tubercular; the parietal 

 .tooth is of good size, elevated, narrow, oblique, and extends 

 from the upper part of the parietal wall almost to the basal ter- 

 mination of the peristome; the parietal tooth is directed to a 

 point between the two teetJi on the outer lip; peristome reflected, 



FIG. 16. 

 Apertures of POLYGYRA. (After Pilsbry.) A, TRIDENTATA Say; B, 



FRAUDULENTA. Pilsbry. 



white, thickened, sometimes grooved; umbilicus widely open, 

 exhibiting all the volutions; base of shell convex (Fig. 16, A). 

 Greater diam., 15.00; lesser, 13.00; height, 7.00; umbilicus, 2.75 mill. (8447.) 



Animal: As usual in the genus; color yellowish-white on 

 foot, darker on sides of body and neck, and jet black on eye- 

 peduncles and tentacles; mantle collar yellowish; the foot is 

 not very long and is rather wide, and the lateral expansions 

 are very pronounced; posteriorly it terminates rather acutely 

 and anteriorly it is truncated; the animal appears much too 

 small for the shell. The foot measures about 20 mill, in length 

 and about 4 mill, in width when the animal is in motion. Heart 

 pulsations regular, eighty-five to ninety per minute. When the 

 animal was partly retracted within its shell the heart beat thirty- 

 three to fifty-five times per minute. 



Jaw: Arched, low, wide, ends blunt; anterior surface 

 with eleven ribs which denticulate both margins. 



Radula formula: V + V+t+V + V ( 25 ~ 1 ~ 25 )- Central 

 tooth with a rather wide base of attachment, the lower outer 

 corners expanded and the lower margin excavated; reflection 

 tricuspid, the center cusp long, reaching to the lower border 



