CLASS GASTROPODA (Concluded) 
Family CERITHIIDAE 
Genus DIASTOMA Deshayes, 1861 
Shell turreted, whorls with numerous transverse ribs, and with a few 
intermediate varices. Inner margin of the aperture partially detached from 
the previous whorl; the aperture itself is strongly contracted posteriorly. 
(Tryon, Structural and Systematic Conchology.) 
Type. ? 
Distribution. California, Pleistocene, of Santa Barbara, California. 
Diastoma oldroydae Bartsch, 1911 
Plate 73, fig. 2 
Proceedings of the Vailed States National Museum, 39:583; fig. 3. 
Shell broadly conic, light brown. Nuclear whorls decollated, post- 
nuclear 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 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, addi¬ 
tional 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 rec¬ 
tangular, depressed areas, having their long axes parallel with their spiral 
sculpture. Periphery of the last whorl marked by a shallow sulcus. Base 
moderately long, well-rounded, marked by six equal and equally spaced, 
spiral cords, the axial sculpture being represented by incremental lines only. 
Sutures channeled. Aperture irregular, large, decidedly channeled and 
somewhat twisted anteriorly; posterior angle obtuse; outer lip moderately 
thin, showing the external sculpture within by transmitted light; columella 
very strongly curved and revolute; parietal wall covered with a thick callus 
which renders the peritreme complete. A strong, white varix is present 
about a quarter turn behind the lip. Length, 3.8; diameter, 1.6 mm. 
(Bartsch.) 
Type in United States National Museum, No. 213024. Type locality, 
San Pedro, California. 
Range. Known only from type locality. 
[611 1 
[9 
