70 
MARINE SHELLS OF WEST COAST OF NORTH AMERICA 
Melanella lastra Bartsch, 1917 
Plate 42, fig. 3 
Proceedings of the United States National Museum, 53:321; PI. 40, fig. 3. 
Shell small, conic, only very slightly flexed; bluish-white, semi- 
translucent; polished, marked by exceedingly fine lines of growth only. 
The first three whorls well-rounded, separated by a well-impressed suture, 
the rest very slightly rounded, with a scarcely defined suture. Periphery 
well-rounded. Base short, well-rounded. Aperture very broadly oval; 
posterior angle acute; outer lip decidedly protracted a little anterior to 
the middle; inner lip short, curved, reflected over and appressed to the 
base; parietal wall covered with a thick callus. This species is similar 
to M. peninsularis, but is uniformly more slender, with the varices much 
less conspicuously marked. The type, an adult shell, which has lost 
probably the first two whorls, retaining eight, measures: length, 4.1; 
diameter, 1.6 mm. (Bartsch.) 
Type in United States National Museum, No. 105519. Type locality, 
Point Abreojos, Lower California. 
Range. San Pedro, California, to Magdalena Bay, Lower California. 
Melanella thersites Carpenter, 1864 
Plate 47, fig. 2 
Supplementary Report, British Society for the Advancement of Science, 286, 659. 
Proceedings of the United States National Museum, 53; PI. 41, figs. 1, 2, 3. 
E. testa parva, curtissima, albida, arcuata, valde distorta; marginibus 
spirae dextro subrecto, sinistro valde excurvato; anfr. nucl. ? .... (decol- 
latis) ; norm, vi., laevibus, subplanatis, suturis distinctis; basivalde arcuata; 
apertura subovali, dextrorsum producta; peritremate continua, valde cal¬ 
losa; labro sinuato. Long., .21; long, spin, .13; lat., .09 poll. (Carpenter.) 
Shell broadly conic, rather stout and heavy, polished, shining, usually 
flexed in one direction only, though sometimes in two. Whorls rather 
strongly rounded, marked by exceedingly fine incremental lines and ir¬ 
regularly scattered varices only. Sutures strongly marked. Periphery of 
the last whorl somewhat inflated, well-rounded. Base short, well-rounded. 
Aperture oval; posterior angle acute; outer lip thick within, sharp at the 
edge, and decidedly protracted a little anterior to the middle; inner lip 
stout, slightly curved, the posterior half reflected over and appressed to 
the base. Parietal wall covered by a very thick callus which renders the 
peritreme complete. Type has lost the earlier whorls; the remaining meas¬ 
ure: length, 5.1; diameter, 2.5 mm. (Bartsch.) 
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