1898.] NATURAL SCIENCES OF PHILADELPHIA. 241 



Body cavity extending into the foot, but frequently not to its end ; 

 genital system and gut lying side by side and extending about the 

 same distance backward (PI. XI, fig. 34, P. fasciatum) . 



Jaw weak, flexible; flatly ribbed, plaited or striate. Rachidian 

 teeth tricuspid, laterals bicuspid, the ectocones small ; marginals 

 formed by shortening of the basal-plates, bicuspid, the mesocone 

 moderate or short, ectocone small, occasionally bifid. 



Intestinal tract (PI. XI, figs. 28, P. Andersoni ; fig. 30, P. coeruleum, 

 fig. 32, P. foliolatum, and fig. 34, P. fasciatum) with four well devel- 

 oped sigmoid folds ; no division of G 1 into crop and stomach ; ante- 

 rior loop formed by G 2 and G 3 twisted one-half revolution ; poste- 

 rior loop of G 3 and G 4 long, extending far behind stomach, and 

 twisted less than a complete revolution. 



Genital system (PI. XII, figs. 37-40, and PI. XIII, all figs.) 

 not crowded forward; no penis nor retractor; epiphallus either 

 very stout, cylindrical and fleshy, with minute perforation, or more 

 slender, long and tapering distally ; in either case suddenly narrow- 

 ing near the atrium to a minute duct, which enters the atrium by a 

 short tapering peduncle, in close contact with which the enlarged 

 epiphallus is held by a muscle (seen in fig. 57 of PI. XIII, muse, and 

 fig. 39 of PI. XII). Duct of spermatheca short ; spermatophores as 

 in Hesperarion. Ovotestis (PI. XI, fig. 34 ) lying anterior to the 

 posterior loop of gut, between its upper and lower folds, adjacent 

 to the albumen gland. 



Muscle system (PI. XIV, fig. 70) with the eye retractors inserted 

 at the outer posterior angles of the diaphragm, as in Arion; buccal 

 retractor inserted at the posterior edge of diaphragm to the right of 

 the middle, bifurcate distally. Right eye retractor passing between 

 branches of genitalia. 



Pallial region (PI. XV, fig. 80) much as in Arion; breathing 

 pore, anus and nephridial orifice at the right anterior angle of the 

 pallial cavity ; kidney ring-like, excavated to show both chambers 

 of the heart; other features as usual in the family. 



Distribution : Middle California to British Columbia, eastward 

 in Idaho to the Cceur d'Alene Mts. 



Prophjsaon stands rather isolated in the Arionince. The only 

 native American genus approaching it is Anadenulus, but this differs 

 in several important particulars to be mentioned below. The Pala?- 

 arctic Arion is like Prophysaon in the pallial region, but differs 

 markedly in (1) the removal of the buccal retractor insertion back- 



