300 TERRESTRIAL AIR-BREATHING MOLLUSKS. 



more commonly in hillside pastures, under flat stones, a situation where other 

 species rarely occur. Two individuals are commonly found together. 



Fig. 194 is drawn from a curious pathological specimen. The peristome 



having been broken after the animal's arrival at maturity, a new peristome has 



been formed somewhat in the rear of the first, and a new parietal 



P ig^l9 4. tooth added. The base of the shell was purposely broken to show 



the position of the internal tubercle. 



The jaw of S. monodon is slightly arcuate, stout, bluntly rounded 



s.lnonodon. at en( l s > anterior surface with broad, stout ribs denticulating each 



margin (Fig. 188). 



H. monodon (PI. VII. Fig. H) has 21 — 1 — 21 teeth on its lingual membrane; 



10 perfect laterals ; the thirteenth tooth has a bifid inner cutting point. Morse 



gives 28—1—28 teeth. 



The characteristic feature of the genitalia is the penis sac. It is unpropor- 

 tionally long, club-shaped, and greatly enlarged above, where it receives both 

 vas deferens and retractor muscle. The genital bladder is small, elongate- 

 oval, on a short, delicate duct. The epididymis is convoluted in its whole 

 length (PI. XI. Fig. L). 



Stenotrema germanum, Gould. 



Vol. HI. PI. XL. a, Fig. 3. 



Shell imperforate, solid, depressed, low-conical above, convex beneath, 

 slightly angular at periphery, covered with a scabrous rusty horn-colored epi- 

 dermis, beset with scattered hairs ; whorls b\, closely revolving, separated by a 

 well-impressed suture ; aperture lunate, the basal portion being but slightly 

 curved, and turning upward at a rather sharp angle; peristome incumbent, 

 with a deep stricture behind it, moderately reflexed, roseate ; on the parietal 

 wall of the aperture is a distinct, oblong, erect, white tooth, not connected with 

 either extremity of the peristome. Greater diameter, 7^ mill. ; height, 5 mill. 



Helix germana, Gould, U. S. Expl. Exped. Moll. (1852), 70, Fig. 40, a, b, c ; 



Terr. Moll., II. 156, PI. XL. a, Fig. 3. — Pfeiffer, Mon. Hel. Yiv., III. 269. 



— W. G. Binney, Terr. Moll. U. S., IV. 11 ; L. & Fr.-W. Sh.,.I. 120 (1869). 

 Stenotrema germana, Tryon, Am. Journ. Conch., III. 58 (1867). 



Oregonian region at Astoria. 



Jaw more resembling the type usual in the subgenus Stenotrema than Meso- 

 don, the ribs, 11 in number, ' being broad and crowded. There are forms 

 of germana closely connecting the species with Mesodon Columbianum, Lea. I 

 have, while treating the latter species (see below), pointed out the decided spe- 

 cific differences shown in the jaw and genitalia; at the same time I have stated 

 that by the want of the internal tubercle, germanum is more nearly allied to 

 Mesodon than to Stenotrema. 



S. germanum (PI. VII. Fig. G) has 28—1—28 teeth; 12 perfect laterals. 



The left-hand figure shows one of the few marginals which have the outer 

 cusp bifid. 



