NO. 1903. WEST AMERICAN PYRAMIDELLID MOLLUSKS—BARTHCH. 273 



of these shows the hrations strongly within the aperture ; in the other, 

 the greater part of the callus which should contain them has been 

 broken away. 



The figured specimen, which is in the United States National 

 Museum, Cat. No. 211552, U.S.N.M., has eight whorls remaining 

 which measure: Length, 7.5 mm.; diameter, 2.1 mm. The other 

 specimen is in Mr. Kelsey's collection. 



This species follows Turhonilla (Mormula) amhusta in the key. 



ODOSTOMIA (BESLA) EXCOLPA, new species. 

 Plate 36, fig. 6, 6a. 



Shell very small, semitranslucent, bluish-white. Nuclear whorls 

 quite large, 2^, forming a moderately elevated, helicoid spire, whose 

 axis is at right angles to that of the succeeding turns, in the first of 

 which it is about one-fourth immersed. Post-nuclear w^horls decid- 

 edly rounded, with the greatest convexity falling on the anterior 

 third of the whorls, between the sutures, appressed at the summit, 

 marked by decidedly sinuous, slender, axial ribs, of which about 18 

 occur upon the first and second, 20 upon the third, and 28 upon the 

 penultimate turn. Intercostal spaces about three times as wide as 

 the ribs. In addition to the axial sculpture, the whorls are crossed 

 by tlirce equal and subequally spaced, spiral threads, which are 

 almost as strong as the axial ribs. The first of these is situated at 

 the posterior termination of the anterior third, between the sutures, 

 wliile the third marks the periphery, the second being halfway 

 between the two. The intersections of the spiral threads and axial 

 ribs are shghtly nodulose, while the spaces inclosed between them 

 appear as almost square pits. Base well rounded, marked by four 

 slender, spiral threads and the feeble continuations of the axial ribs, 

 which extend to the umbiUcal area. Sutures strongly impressed. 

 Aperture ear-shaped; posterior angle acute; outer lip thin, showing 

 the external sculpture within; inner hp shghtly curved, decidedly 

 revolute, adnata to the base, provided with a strong, obliquo 

 fold at its insertion ; parietal wall covered with a thick callus, which 

 connects the insertion of the inner hp with the posterior angle of 

 the aperture. 



The type (Cat. No. 198903fj, U.S.N.M.) was coUected by Dr. 

 Edward Palmer at the head of the Gulf of Cahfornia. It has five post- 

 nuclear whorls and measures: Length, 2 mm.; diameter, 0.7 mm. 



The present species recalls Odostomia (Besla) convexa Carpenter, 

 from which it differs in having the whorls much more rounded and 

 in having the ribs decidedly flexuose, and four instead of eight spiral 

 threads on the base. 



20441°— Proc.X.M.vol.4:i—lli 18 



