144 THE CHICAGO ACADEMY OF SCIENCES. 



Animal: As usual in the genus; generally dark bluish or 

 slate colored, but blackish on the head and eye-peduncles, 

 which are long and slender; foot long and narrow, broadly 

 rounded before and acutely pointed behind. 



Jaw: Of the usual form, rather thick and broad with four 

 teen heavy ribs. 



Radula formula Y+i+i+l+V 1 (22-1-22); teeth of the 

 same type as tridentata, but the inner cusps of the marginal 

 teeth are all simple. Occasionally a stray tooth will have a 

 bifid inner cusp, as the twentieth in one membrane and the 

 twenty-first and twenty-third in another (vide Binney for the 

 last). 



Genitalia: "Generally resembling those of tridentata, but 

 distinguished by the genital bladder, which is small, globular, 

 on a duct of equal width throughout its course, not swelling as 

 it approaches the vagina." (W. G. Binney.) 



Distribution: Pennsylvania west of the Alleghany Moun- 

 tains, west to Illinois, south to Sea Islands of Georgia, Ala- 

 bama, Mississippi and Indian Territory. (Pilsbry.) Michigan. 

 (Walker.) 



Geological distribution: Pleistocene; Loess. 



Habitat: Similar to that of P. tridentata. 



Remarks: This species is at once distinguished by its ap- 

 erture and closed umbilicus. It seems to be the rarest of our 

 Helices, and it may be that the two specimens collected by 

 Professor Higley at Miller's, Ind., were introduced from some 

 point in Michigan. It has not yet been found in any other 

 locality. 



52. Polygyra tridentata Say, pi. xxx., fig. 6. 



Helix tridentata SAY, Nich. Encyl., pi. ii., fig. 1, 1817, 1819. 



Triodopsis lunula RAFINESQUE, Enumer., p. 3. 



Polygyra tridentata juxtigens PILSBRY, Proc. Phil. Acad., p. 20, 1894 



(Variety.) 

 Polygyra tridentata edentilabris PILSBRY, The Nautilus, Vol. VII. 



p. 140, 1894. (Variety.) 

 Polygyra tridentata complanata PILSBRY, 1. c., Vol. XII., p. 22, 1898. 



(Variety.) 

 Polygyra tridentata bidentata BAKER, Trans. Acad. Sci., St. Louis, 



Vol. VIII., p. 85, 1898. (Variety.) 

 Polygyra tridentata unidentata BAKER, 1. c., p. 85, 1898. (Variety.) 



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

 face covered with very heavy raised oblique striae, the apical 

 whorls smooth; color, horn, inclining to reddish; periphery 



