28 PROCEEDINGS OF THE Ni^.TIONAL MUSEUM Vol.70 



steadily in strength until on the last turn they form decidedly raised 

 sinuous ridges. The last whorl, too, shows well-marked malleations. 

 Aperture oval; posterior angle obtuse; inner lip curved and re- 

 flected, but not appressed to the base; parietal wall covered by a 

 thick callus. 



The type, Cat. No. 213369, U.S.N.M., was collected by Dr. S. S. 

 Berry in 40 fathoms, off Catalina Island, California. It has lOi^ 

 whorls and measures, length, 5.3 mm.; diameter, 1.9 mm. It is at 

 once divstinguished from the other two West American species by the 

 absence of incissed spiral lines. 



AMPHITHALAMUS STEPHENSAE, new species 



Plate 4, fig. 5 



Shell minute, pale brown with an ashy tinge except the columellar 

 region which is flesh colored; the early whorls when they contain 

 the animal are much more dusky. Nuclear whorls 1.5; the first 

 half smooth, the rest marked b}'^ rather distantly spaced, poorly 

 developed, rather broad spiral lirations of which nine are present 

 between the summit and the periphery. In addition to this, there 

 are inconspicuous lines of growth. Postnuclear whorls strongly 

 rounded, narrowly shouldered at the summit, the portion appressed 

 to the preceding turn appearing through the substance of the shell 

 as a band. Periphery with a weak keel which is truncated rather 

 abruptly posteriorly but grades gently into the substance of the shell 

 toward the base. Suture well marked. Base short, inflated, strongly 

 rounded, marked by lines of growth only. There is a heavy callus 

 at the insertion of the columella, which at its posterior termination 

 almost forms a cord. The columella itself is very heavy and oblique. 

 The conformation of the aperture is characteristically Amphithalmid, 

 that is, the aperture which is oval is much contracted by having a 

 shelf extending out from the columellar and the parietal wall to- 

 ward the outer lip, contracting the aperture. This shelf forms a 

 decided pit behind its edge. The inner and parietal lip of the 

 aperture, therefore, are not in contact with the columellar or the 

 parietal wall, but at some distance from it; the posterior portion 

 of the outer lip, however, extends upward to the preceding turn, 

 which it joins immediately below the peripheral keel as in mollusks 

 with a normal aperture. Operculum thin, paucispiral. 



The type. Cat. No. 348531, U.S.N.M., was collected by Mrs. C. L. 

 Simons in Magdalena Bay, Lower California. It has four whorls, 

 and measures, length, 1.1 mm. ; greater diameter, 0.9 mm. Cat. No. 

 348532, U.S.N.M., contains an additional lot of specimens taken from 

 kelp root in Turtle Bay by Mrs. Simons. 



