NO. 2331. WEST AMERICAN MOLLUSKS—BARTSCH. 161 



whorls depressed. Whorls four, convex, slightly shouldered at the 

 summit. Aperture suboval. Operculum thin, translucent. To the 

 above description, which is based upon Carpenter's diagnosis and 

 camera lucida figure. Carpenter's remarks, which are as follows, may 

 be added: 



Differs from the least elevated form of Jcffreysia hifnsciata in its very swell- 

 ing and somewhat irregular whirls, transparent white texture, and large angu- 

 lated umbilicus. The operculum, which was found in 5 out of the 13 specimens, 

 is perfectly transparent, appearing black from the remains of the animal, which 

 seems to have been differently coloi*ed from that of J. bifasciata. Long. .048 

 (1.2 mm.), long. spir. .026, lat. .038 (95 mm.). 



Hab., Mazatlan; very rare, off Chama and Spondylus ; Liverpool Col. [British 

 Museum]. 



Tablet 1719 contains 2 sp. ; one young and glossy, with the operculum so sit- 

 uated as to show the medial process ; the other adult. 



RISSOELLA EXCOLPA. new species. 



Plate 12, fig. 3. 



Shell small, flesh colored, inflated ovoid. Whorls strongly rounded, 

 appressed at the summit, marked by numerous closely spaced, decid- 

 edly retractively slanting axial threads which pass over the inflated 

 and well-rounded periphery as well as the well-rounded base. Base 

 narrowly umbilicated, the posterior edge of the umbilicus slightly 

 angiilated. Aperture very broadly oval; posterior angle obtuse; 

 outer lip thin, showing the external sculpture within; inner lip 

 strongly curved and but very slightly reflected ; parietal wall covered 

 by a thick callus, which renders the peritreme complete. 



The type and two specimens. Cat. No. 267502, U.S.N.M., were 

 collected by the author at head of Concepcion Bay, Lower California. 

 The type has four whorls and measures — length, 2.5 mm. ; diameter, 

 1.8 mm. 



Our specimens do not have an operculum, but we are led to believe 

 that they belong to this genus. In general form of outline and also 

 in the matter of umbilicus it suggests Rissoella tumens Carpenter, 

 Carpenter's description, however, does not mention the axial thread 

 sculpture and his figure gives a much wider umbilicus than our 

 specimens possess. 



RISSOELLA ANGULIFERENS (de Folin). 



Plate 12, fig. 9. 

 1870. Rissoa anguUferens de Folin, Fonds de la Mer, vol. 1, p. 134, pi. 20, 

 fig. 6. 



Shell small, conic, polished, yellowish brown with a broad whitish 

 band which gradually shades into the darker coloration. Nuclear 

 181404— 21— Proc.N.M.vol.58 11 



