CLASS GASTROPODA 
85 
Shell elongate-ovate, purplish brown with the nuclear whorls yellowish 
white. Nuclear whorls about one and one-half, well-rounded, marked by 
about 15 slender, equal and equally spaced, spiral threads and numerous 
very fine, axial threads, lending the surface a very minutely pitted appear¬ 
ance. Post-nuclear whorls subtabulately shouldered at the summit, well- 
rounded on the middle, marked by fine lines of growth only. Suture well- 
impressed. Periphery of the last whorl marked by a rather broad, low, 
rounded, spiral thread, which is separated from the space posterior to it 
by a narrow, shallow, spiral sulcus. Anteriorly, this cord passes, without 
demarcation, into the general surface of the moderately long and gently- 
rounded base. Base broadly umbilicate, having a rather broad, low, spiral 
cord a little posterior to the insertion of the columella. Aperture oval, very 
oblique, re-enforced within by an inner peristome, which, in the anterior 
portion of the outer lip, fuses with it, while the columella portion and the 
parietal portion stand at a considerable distance from the columella and 
the parietal wall, being connected with these by a concave bridge of shelly 
matter; columella moderately long and stout. Length, 1.4; diameter, 0.9 
mm. (Bartsch.) 
Amphithalamus lacunatus Carpenter, 1866 
Proceedings of the California Academy of Sciences f 3:218. Proceedings of the United 
States National Museum , 41: 263; fig. 1. 
A. t. adolescente A. incluso simili; nucleo similiter minutissime et 
confertissime spiraliter et radiatim striulato; sed majore, latiore, anfr. 
subplanatis; basi late lacunata, baud carinata; adulta?—Long., 0.06; long, 
spir., 0.03; lat., 0.03 poll. (Carpenter.) 
Shell minute, broadly conic, milk-white. Nuclear whorls one and one- 
half, well-rounded, marked by about 15 slender, equal and equally spaced, 
spiral threads and numerous, very fine, axial threads, lending the surface 
a very minutely pitted appearance. Post-nuclear whorls feebly shouldered 
at the summit, slightly rounded, marked by incremental lines only. Suture 
well-impressed. Periphery of the last whorl inflated, rounded. Base mod¬ 
erately long, slightly rounded, with a narrow umbilical chink. Aperture 
incomplete (outer lip fractured); inner lip curved, appressed; parietal 
wall covered with a thick callus. Length, 1.5 ; diameter, 1.1 mm. (Bartsch.) 
Type in United States National Museum, No. 15564. Type locality, 
San Pedro, California, in the shell washings. 
Range. Known only from type locality. 
Amphithalamus tenuis Bartsch, 1911 
Proceedings of the United States National Museum, 41:264; fig. 3. 
Shell elongate-ovate, dark greenish horn-color, with the columella and 
the aperture yellowish-white except the dark edge of the peristome. 
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