Abt. 11 NEW AMERICAN MARINE MOLLUSKS — BARTSCH 3 



ings and fulgurations of brown. Nuclear whorls smooth. Post- 

 nuclear whorls appressed at the summit, marked by vei*y fine lines 

 of growth which are almost vertical, and numerous, closely spaced, 

 microscopic spiral striations. Suture very slightly constricted 

 Periphery of the last whorl well rounded. Base long, moderately 

 rounded; columella marked by eight feebly developed spiral cords. 

 Aperture large; posterior angle acute, decidedly channeled ante- 

 riorly; outer lip thin showing the external markings within; inner 

 lip sinuous ; parietal wall covered with a thin callus. 



The type, Cat. No. 362456, U.S.N.M., was collected by Dr. K. H. 

 Tremper on rocks at San Clemente Island, California. It has 

 five and one-half whorls and measures, length, 3.2 mm.; diameter, 

 1.5 mm. 



A topotype is in Doctor Tremper's collection. Cat. No. 211060, 

 U.S.N.M., also contains one collected by S. A. L. Brannan on Cata- 

 lina Island. 



This species is nearest related to Astyris aurantiaca Dall, but is 

 uniformly smaller. 



OPALIA TREMPERI, new species 



Plate 1, fig. 8 



Shell moderately large, milk white. Nuclear whorls decollated. 

 Postnuclear whorls marked by poorly developed, retractively slanting 

 axial ribs which terminate at the summit in a series of cusps. Sev- 

 eral ribs frequently fuse to form a single cusp. The ribs on the first 

 two turns of the type are obsolete, on the third 20 are present, while 

 the fourth has 22, the fifth 24, the sixth and last have 26. In addition 

 to the axial sculpture there are also obsolete varices at irregular in- 

 tervals. The entire surface of the spire is marked by narrow spiral 

 cords. The spaces that separate these cords are crossed by numerous, 

 very slender, axial threads which give them a decidedly pitted ap- 

 pearance. Suture slightly constricted. Periphery of the last whorl 

 well rounded. Base rather attenuated, marked by the continuations 

 of the axial ribs and the same type of spiral sculpture described for 

 the spire. Aperture large, decidedly oval, with a strongly expanded 

 and thickened peristome; outer lip evenly curved; inner lip almost 

 straight and continuing as a heavy callus over the parietal wall which 

 renders the peritreme complete. 



The type. Cat. No. 362454, U.S.N.M., was collected by Dr. K. H. 

 Tremper on rocks at San Clemente Island, California. It has seven 

 and one-half whorls and measures, length, 7.8 mm. ; diameter, 2.5 mm. 



