334 TERRESTRIAL AIR-BREATHING MOLLUSKS. 



Moll., 46 (1843). PFEIFFER, Mon. Hel. Viv., I. 343; in CHEMNITZ, ed. 2, 

 I. 332, PI. LVIII. Figs. 10 - 12 (1846). REEVE, Con. Icon., No. 692 (1852). 

 BINNEY, Terr. Moll., II. 169, PI. V. W. G. BINNEY, Terr. Moll., IY. 

 16 ; L. & Fr.-W. Sh., I. 150 (1869). 



Helix labiosa, GOULD, Proc. Bost. Soc. Nat. Hist., II. 165 (1846) ; U. S. Expl. 

 Exped. Moll., 67, Fig. 35 (1852) ; Terr. Moll., II. 170, PI. XIII. a, Fig. 1. 

 PFEIFFER, Mon. Hel. Viv., I. 343 (included in Columbiana in Vol. V.). 



Mesodon Columbiana, TRYON, Am. Journ. Conch., III. 46 (1867). 



A species of the Pacific province ranging from Sitka and Fort Simpson (lat. 

 54 40') to Santa Cruz in California (lat. 37 20'). 



Animal slender, eye-peduncles and tentacles much elongated. Color pale 

 ferruginous, with a lilac tint, darker on the neck. Whole surface, even the 

 eye-peduncles, marked with coarse, elliptical granules, in longitudinal series; 

 no marginal border. 



There is a variety with a well-developed parietal tooth. 



I formerly had difficulty in separating certain forms of Mesodon Columbiana, 

 Lea, and Slenotrema germanum, Gould, but have recently received, through the 

 kindness of Mr. Henry Hemphill, specimens of both species, preserved in alco- 

 hol, from several distinct localities. An examination of their soft parts has 

 proved that in the jaw and genital system there exists a specific difference 

 readily detected. This difference appears to be constant, as I have observed 

 it in one specimen, with parietal lamina and quite depressed, of Columbiana, 

 from San Leandro, California, and three from another locality. In germanum 

 I also have found the characters constant, having examined four specimens, 

 one from Astoria, the other three from a separate locality. 



In the jaw the distinction is in its general outline and in the size and fre- 

 quency of the ribs on the anterior surface. In germanum the jaw is slightly 

 arcuate ; the ribs are about 1 1 in number, broad, crowded, with narrow inter- 

 stices only, generally resembling the jaw found in Slenotrema. In Columbiana 

 the jaw is more arched, the ribs are less numerous, about 8, narrower, much 

 more separated, and more decidedly produced on either margin, as usual in 

 Mesodon. For figures of the jaw of each see Ann. N. Y. Lye. Nat. Hist. X. 

 PI. XIV. 



In the genitalia the difference lies in the genital bladder. This organ in 

 Columbiana (PI. XI. Fig. I) is clavate, short, with a short, stout duct, but in 

 germanum (Fig. M) it is globular, and has a long, narrow duct. 



In both species the retractor muscle of the penis is attached to the vas def- 

 erens a short distance before the latter organ enters the penis sac, which it 

 does at the apex of the latter. 



Jaw (see above). 



Lingual membrane (PI. VIII. Fig. P) with 33 1 33 teeth; 15 laterals, the 

 sixteenth tooth having a bifid cutting point. There are decided side cusps and 

 cutting points to the central and lateral teeth. 



