NO. 1802. 



WEST AMERICAN DIA8T0MA—BART8CH. 



583 



Fig. 2.— Diastoma 

 cheysalloidea 

 Babtsch. 



The same number and disposition of bands occurs upon the third turn, 

 but here the first subperipheral band becomes apparent in the suture. 

 This arrangement holds good on the next turn. On the fifth post- 

 nuclear whorl an additional slender cord appears between the first 

 and second and another between the second and 

 third cords, which on the penultimate turn assume 

 the strength of the adjacent members. The inter- 

 sections of the spiral cords and the axial ribs form ill- 

 defined tubercles. Sutures strongly impressed; peri- 

 phery and base of the last whorl well rounded, the 

 latter marked by seven equal and equally spaced, 

 low, spiral cords, which are almost as wide as the 

 spaces that separate them. In the intervening 

 grooves many slender, axial threads are present. 

 Aperture irregularly ovate, large, decidedly ex- 

 panded at the junction of the outer and basal lips, 

 channeled anteriorly; posterior angle acute; outer 

 lip thin at the edge where the spiral cords appear as 

 brown spots on a yellowish, white background; 

 columella short, moderately strong; appressed to 

 and reflected over the attenuated base; parietal wall 

 covered with a very thick callus which merges into 

 the columellar edge and renders the peritreme complete. A strong 

 varix is present about one-fourth of a turn behind the aperture. 

 The type (Cat. No. 73996, U.S.N.M.) has seven post-nuclear whorls 

 and measures: Length, 6.3 mm.; diameter, 2.4 mm. It comes from 

 the Gulf of Califorina. 



DIASTOMA OLDROYD.^;, new species. 



Shell broadly conic, light brown. Nuclear whorls decollated, 

 postnuclear whorls slightly rounded, shouldered at the summit, 

 marked by weak, axial ribs, of which sixteen occur 

 upon the fourth and fifth, eighteen upon the sixth and 

 the penultimate turn. Intercostal spaces about twice 

 as wide as the ribs. In addition to the axial ribs the 

 whorls are crossed by four slender, poorly developed, 

 spiral cords, the intersection of which, with the ribs, 

 renders them feebly nodulose. On the last whorl a 

 slender, additional thread appears between the cord at 

 the summit and the one adjacent to it. The spaces 

 inclosed between the ribs and the spiral cords are rect- 

 angular, depressed areas, having their long axes 

 parallel with their spiral sculpture. Periphery of the 

 last whorl marked by a shallow sulcus. Base mod- 

 erately long, well rounded, marked by six equal and equally 

 spaced, spiral cords, the axial sculpture being represented by incre- 



FiG. 3.— Diasto- 

 ma OLDROTD^ffi 



Bartsch. 



