340 PROCEEDINGS OF THE ACADEMY OF [1896. 



EXTERNAL CHARACTERS. 



The external characters of Ariolhnax ^\\d Aphallarion are de- 

 scribed below. Arion differs from these American groups in the 

 rounded, not keeled, back, the anterior breathing pore and the more 

 posterior genital orifice. 



JAWS AND TEETH. 



The jaw in Arlolimax and Aphallarion is of the ribbed type 

 usual in Arionidce, and does not differ materially from that of Arion. 

 The teeth offer no characters of generic importance, being of the 

 general type found throughout Arionidce. Those of the median part 

 of the radula are of the Helicid form ; the marginal teeth develop 

 long mesocones, simulating somewhat the teeth of Zonitidce, precisely 

 as those of some Endodontidce do. 



DIGESTIVE SYSTEM. 



In Arion, Arlolimax ■o.ndi Aphallarion the alimentary canal is dis- 

 tinctly differentiated into fore-, mid- and hind gut. The short oesopha- 

 gus leads into a capacious crop, ivhich is separated by a decided 

 constriction from the stomach, which lies near the posterior end 

 of body. At the termination of the stomach the bile duct enters, 

 near the origin of the intestine. The latter presents, after coiling 

 spirally once around the visceral mass, an anterior loop, lying to the 

 right of the albumen gland. Passing backward it coils in a reverse 

 direction around the visceral mass and forms a posterior loop, which, 

 in the American forms (PI. XIII, figs. 2, 4) lies behind, in the Eur- 

 opean (Arion, PI. XIII, fig. 3) above and anterior to the main mass 

 of the stomach. From this loop the intestine passes forward, describ- 

 ing a spiral coil again reversed in direction, and terminates near the 

 respiratory orifice on the right side of the body anteriorly. 



The digestive systems of the three genera Arion, Ariolimax and 

 Aphallarion differ only in subordinate features. In Arion, the 

 stomach, as mentioned above, lies behind the posterior loop of the 

 hind-gut. In Ariolimax and Aphallarion the posterior loop lies 

 behind the stomach. Aphallarion differs from the other two genera 

 in having a spiral turn less of the intestine. As usual in slugs 

 there are four lengthwise folds of the gut. 



A very long and (for a slug) complexly disposed intestine, and a 

 complete separation of crop and stomach, are the peculiar charac- 

 teristics of these great slugs. This will become more apparent when 



