1903.] NATURAL SCIENCES OF PHILADELPHIA. 627 



posterior third and fourth of its length. One of the largest individuals 

 measures, length 14, breadth of sole 1.3 to 1.5, length of mantle 

 5.5 mm. In more contracted individuals the sole is somewhat broader 

 in front. 



The wholly buried shell is calcareous and moderately strong, oblong, 

 a little convex, the left side more straightened than the right, the 

 slightly projecting blunt apex being terminal. The surface is marked 

 with growth-strige, and seems to be without periostracum. Length 

 2.5, width 1.5 mm. 



The free retractor muscles are arranged as in Hesperarion and its 

 allies, the ocular retractors and the pharyngeal retractor being inde- 

 pendent bands converging to the posterior edge of the mantle-cavity 

 where they are inserted in a group (PI. XXVIII, fig. 6). 



The genitalia (PI. XXVIII, fig. 5) were imperfectly worked out.^ 

 The penis (p.) is a stout, oblong sac receiving the vas deferens a little 

 distad of the middle of its length, and its lumen is there contracted by 

 a fleshy transverse body or sort of valve. Above this the walls are 

 thicker. Both divisions are smooth within. The small spermatheca 

 {sip.) is defined by a constriction from the duct {sp. d.), which is a 

 very capacious sac, longer than the penis, opening directly into the 

 atrium. Internally this relatively enormous duct has a few coarse 

 longitudinal folds, the number increasing toward the distal end where 

 they are numerous. Its structure, aside from size, is therefore what 

 is ordinarily encountered. 



No retractor muscle of the penis was seen, probably owing to the 

 ill preservation of the specimen, or to imperfect attention in the 

 early stage of the dissection. The terminal duct only of the ? system 

 could be traced {ov.). 



The alimentary canal is constructed on the usual Arionid type, 

 though less twisted than in the related genera. The jaw is opaque, 

 very thin, arcuate, and composed of numerous dark plaits or flat ribs 

 separated by thin, transparent, much narrower intervals. In one 

 specimen examined there are over twenty-five narrow ribs (PI. XXVIII, 

 fig. 3); in another the ribs are much wider and not so numerous (PI. 

 XXVIII, fig. 2). 



The crop is long and capacious, hardly separated from the stomach. 



The intestine (PI. XXVIII, fig. 4) is of the usual four-folded type 

 the anterior loop caught in the cephalic artery. It is curved in figure 



' The spirit first used on the specimens was apparently too weak to properly 

 preserve the viscera; and the genitalia and intestine were so soft and tender that 

 their dissection was difficult. 



