1898.] NATURAL SCIENCES OF PHILADELPHIA. 221 



saon and Avion this plate is largely cuticular, the calcareous layer 

 being represented only by scattered, angular, granules. In all cases 

 the shell-cavity in the mantle is small, not much larger than the en- 

 closed shell. This contrasts strongly with the allied family Philo- 

 mycicke, which has an enormously extended, empty shell sack. 



General internal topography. — In most genera of completely 

 limaciform external contour, the body from head to tail is excava- 

 ted into one general body cavity (see these Proceedings for 1896, 

 PI. XIII, fig. l),in which the digestive system lies extended, with the 

 genitalia lying parallel with or across it, the liver or liver and ovo- 

 testis extending into the tail. In genera with a dorsal hump (Bin- 

 neya and Hemphillia) that portion of the foot behind the posterior 

 end of the hump is not excavated, but solid as in Helix and other 

 spiral-shelled genera. The liver and ovotestis lie in the posterior 

 portion of the cavity of the hump, into which the viscera are 

 crowded upward and forward. Along the floor of the body cavity, 

 extending from below the mouth a variable distance backward, lies 

 the suboral gland (P. A. N. S., 1896, PI. XIII, f. 1), which in some 

 genera is deeply imbedded in the muscular tissue of the sole, in 

 others lies lightly attached thereto. 4 In Ariolimax and its immedi- 

 ate allies the genital system including the ovotestis, is crowded for- 

 ward into the anterior half of the animal's length ; in Prophysaon 

 and most other genera it lies stretched out at greater length, and 

 the albumen gland and ovotestis are decidedly posterior. Other 

 peculiarities in the arrangement of the organs are noticed below. 



Alimentary tract. — The buccal body in Arionidve is short, as in 

 allied families of snails. The jaw varies from thin and flexible to 

 strong, is of the ordinary arched form, and is always sculptured an- 

 teriorly. The usual sculpture consists of numerous flattened ribs 

 deuticulating the cutting margin ; but in Prophysaon fasciatum the 

 structure is rather a series of narrow, hardly overlapping or imbri- 

 cating plaits, much as in some species of the genus Flammnlina of 

 the Endoclontidce. In P. humile the plaits seem quite lost in 

 a general, close, vertical striation, as in Pyramidula, also a genus of 

 Endodontidce. 



The radula resembles that of the Endodontidoz. The central 

 teeth are tricuspid, ectocones small. Lateral teeth bicuspid, passing 



4 This gland, the function of which is to secrete mucus to lubricate the sole 

 in crawling, was erroneously interpreted as a buccal retractor muscle by 

 Binney, Man. Amer. Land Shells, p. 98, second paragraph from top. 



