CLASS GASTROPODA 
107 
Rissoina dalli Bartsch, 1915 
Plate 83, fig. 2 
Proceedings of the United States Natimial Museum, 49:59; PI. 33, fig. 2. 
Shell small, elongate-conic, subdiaphanous. Nuclear whorls almost 2, 
inflated, well-rounded, smooth. Post-nuclear whorls moderately rounded, 
appressed at the summit, the appressed portion being somewhat excurved, 
lending the whorls the aspect of having a double suture. Whorls marked 
by numerous, very fine, closely spaced, almost vertical, axial threads which 
are about as wide as the spaces that separate them. Suture feebly im¬ 
pressed. Periphery of the last whorl well-rounded. Base moderately long, 
well-rounded, marked like the spire. Aperture moderately large, ovate; 
outer lip somewhat effuse, thick at the edge, thin within where the external 
sculpture is seen through the substance of the shell; inner lip moderately 
thick, strongly curved, reflected over and adnate to the base. Parietal wall 
covered with a thick callus, which renders the peritreme complete. Length, 
2.8; diameter, 1 mm. (Bartsch.) 
Type in United States National Museum, No. 107281. Type locality, 
San Pedro, California. 
Range. San Pedro, California, to South Coronado Island. 
Rissoina coronadoensis Bartsch, 1915 
Plate 83, fig. 8 
Proceedings of the United States National Museum, 49:60; PI. 33, fig. 8. 
Shell small, elongate-conic, milk-white. Nuclear whorls a little more 
than two, well-rounded, smooth. Post-nuclear whorls moderately rounded, 
appressed at the summit, the appressed portion slightly excurved, marked 
by slender, slightly protractive, somewhat sinuous, axial threads of which 
40 occur upon the first, 42 upon the second, 48 upon the third, 56 upon 
the fourth, and 52 upon the penultimate turn. These threads are separated 
by intercostal spaces about as wide as the threads. Suture well-impressed. 
Periphery of the last whorl well-rounded. Base rather short, slightly 
concaved, marked by the continuations of the axial threads, which extend 
undiminished to the umbilical area. Aperture oval, posterior angle acute; 
outer lip thin at the edge, thickened immediately behind the edge by a 
varix, thin, deep within where the external sculpture shines through the 
substance of the shell; inner lip short, strongly curved, reflected over and 
adnate to the base; parietal wall covered with a thick callus, which renders 
the peritreme complete. Length, 3.5; diameter, 1.3 mm. (Bartsch.) 
Type in United States National Museum. Type locality, Coronado 
Islands. 
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