74 



A MANUAL OF AMERICAN LAND SHELLS. 



I have not examined the jaw or lingual membrane of this species, but 

 am entirely dependent on Morse for the descriptions and figures of the 

 American form given above. 



Fig. 34. 



Animal of 77. lineatus, 

 enlarged. (Voise.) 



Fig. 35. 



HELICODISCUS, Morse. 



Animal heliciform; mantle posterior, thin, simple, protected by a 

 shell ; other characters as in Patula. 



Shell discoidal, widely umbilicated, not shining; 

 si)ire concave; whorls 4, equally visible above and 

 below, the last scarcely larger than the rest, not 

 deflected; aperture rounded, vertical; several pairs 

 of tubercles at intervals within, on the inner surface 

 of the outer whorl; peristome simple, straight, its 

 margins distant. 

 Jaw, according to Morse, of S. lineatus, low, wide, crescentic, ends 

 much attenuated, acute; cutting margin with 

 a median, beak-like projection; anterior sur- 

 jaw of H. lineatus. facc without ribs, but covcrcd with striai con- 



verging obliquely towards the beak-like prominence. 



Fig. 36 shows the general arrangement of the teeth upon the lingual 

 Fig. 36. membrane. The characters 

 I of the separate teeth are 

 better shown in Plate IV 

 lof T. M., V, Fig. M. Morse 

 ^ gives 77 rows of 12-1-12 



Lingual dentition of if. ii/ieatws. (ilorse.) teeth Cach witll 4 PCrfcct 



laterals. Leidy, in T. M., Vol. IT, 262, Fig. gives 13-1-13 teeth, with 

 5 i)erfect laterals. The membrane examined by me has 12-1-12 teeth, 

 with 4 perfect laterals. The central teeth have a base of attachment 

 very small, longer than wide, with expanded lower angles and reflected 

 upper margin. Ketiection very small, with a stout, short median cusp, 

 and very short, blunt side cusps, all the cusps with short cutting points. 

 The lateral teeth have a base of attachment three times as wide, and 

 somewhat longer than the centrals, and asymmetrical by the suppres- 

 sion of the inner, lower lateral expansion; the upper margin is broadly 

 reflected; the reflection is short but symmetrical, having two equally 

 developed short, stout side cusps, bearing short cutting points; the 

 median cusp is stout, long, extending nearly to the lower edge of the 

 base of attachment, beyond which projects slightly the short cutting 



