172 THE CHICAGO ACADEMY OF SCIENCES 



64. Circinaria concava Say, pi. xxviii, fig. 4. 



Helix]foncava SAY, Journ. Phil. Acad., Vol. II, p. 159, 1821. 



Helix planorboides FERUSSAC, Hist. Nat. Des. Moll., pi. Ixxxii, fig. 4. 



Helix dissident DESHAYES, in FERUSSAC, Hist. Nat. Des. Moll., Vol. I, 



p. 97, pi. Ixxxiv, figs. 1, 2. 



Shell: Depressed, rounded, almost flat on the upper sur- 

 face; color light yellowish-horn, with a tinge of greenish; sur- 

 face shining, covered with numerous crowded, raised lines of 

 growth; whorls five, rounded below, flat above, the outer whorl 

 somewhat spreading as it approaches the aperture; spire flat 

 or only slightly convex; sutures very deeply excavated as they 

 approach the aperture; aperture rounded-oblique, flattened 

 above by a deflection of the peristome; the aperture is fre- 

 quently tinged with brownish; peristome flattened and de- 

 flected above its junction with the last whorl, the portion near 

 the columella subreflected; columella with a rather thin callus, 

 which connects the two extremes of the peristome; umbilicus 

 wide, deep, spreading, showing all the volutions to the apex; 

 base of shell rounded. 

 Greater diameter, 15.00; lesser, 12.50; height, 6.50; umbilicus, 5.00 mill. 



(10094.) 

 Greater diameter, 14.00; lesser, 12.00; height, 6.50; umbilicus, 4.50 mill. 



(7766.) 



Animal: (Fig. 29.) With a narrow body; anterior portion 

 much in advance of shell; color blackish, mottled with light 



FIG. 29. 

 Animal of CIRCINARIA CONCAVA Say. (After Binney.) 



horn; eye-peduncles long, cylindrical, bluish, eyes at tip, on 

 rounded protuberances; tentacles comparatively long and slen- 

 der, cylindrical; foot obtusely rounded behind, blunt before; 

 creeping disk long and rather broad; head prominent; respira- 

 tory orifice on right side just beneath a point where the per- 

 istome meets the body of the last whorl; contractions of foot 

 strongly marked when viewed through a glass; base of animal 

 dirty white; collar reddish-orange. Length of foot 14.25 mill., 

 with 4.00 mill. 



The heart is situated 5 mill, from the edge of the aper- 

 ture, and is very plainly seen through the transparent shell, 



