CLASS GASTROPODA 
223 
Circulus cosmius Bartsch, 1907 
Proceedings of the United States National Museum, 32:173; fig. 8. 
Shell decidedly depressed, planorboid, creamy white, shining. Nepionic 
whorls 2, well-rounded, helicoid, polished. Succeeding turns marked by a 
low, rather broad, spiral thread at the summit and a strong, acute, lamellar 
ridge at the periphery, and another equally strong halfway between the 
periphery and the summit. The last has the free edge pointing outward, 
forming an angle of 45° with the peripheral lamella. I he spaces between 
these keels are gently rounded and marked by incremental lines only. The 
middle keel forms the most elevated portion on each whorl, the summit of 
the whorl at the suture being considerably lower. Base very broadly um- 
bilicated, marked by a spiral, lamellar carina, which is as strong as the 
peripheral one and is situated halfway between this and the umbilical 
angle. In addition to this carina the entire base shows fine incremental 
lines. Umbilicus limited by an obtuse angle; columellar wall almost verti¬ 
cal, marked by three, slender, equally spaced, spiral lirations. Aperture 
decidedly oblique, pentagonal, the angles being formed by the three 
carinae, the posterior angle of the aperture, and the umbilical angle; outer 
lip thin; columella decidedly curved; parietal wall covered by a strong 
callus, which renders the peritreme almost continuous. Greater diameter, 
2.5; lesser diameter, 2.1; altitude, 1 mm. (Bartsch.) 
Type in United States National Museum, No. 192708. Type locality, 
U.S.S. “Albatross” Station 2799, near Atacames, Ecuador. 
Range. Catalina Island, California, to Ecuador. 
Genus CYCLOSTREMELLA Bush, 1897 
Shell minute, thin, semitransparent when fresh, planorbiform, of few 
convex whorls, nearly symmetrically coiled, forming a concavely depressed 
spire and large umbilical cavity. Epidermis thin, nearly colorless. Nuclear 
whorl relatively large, smooth, turned downward, seen only in a basal view, 
leaving a small pit above. Suture deep and channeled. Aperture triangu¬ 
lar-ovate, expanded below, angulated above, with a relatively wide deep 
sinus just below the suture. Peritreme thin, simple, continuous, not modi¬ 
fied, slightly attached. (Bush.) 
Type. Cyclostremella humilis Bush. 
Distribution. Atlantic and California. 
Cyclostremella californica Bartsch, 1907 
Plate 106, figs. 1, 2, 3 
Proceedings of the United States National Museum, 32:174; fig. 10. 
Shell small, planorboid, semitransparent, closely spirally striated. Ne¬ 
pionic whorls 1J4, moderately rounded, smooth, and shining. Succeeding 
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