. Bulletin - United States National Museum. Science. Animal of 77. lineatus, enlarged. (Voise.) Fig. 35. HELICODISCUS, Morse. Animal heliciform; mantle posterior, thin, simple, protected by a shell; other characters as in Patula. Shell discoidal, widely umbilicated, not shining; si)ire concave; whorls 4, equally visible above and below, the last scarcely larger than the rest, not deflected; aperture rounded, vertical; several pairs of tubercles at intervals within, on the inner surface of the outer whorl; peristome simple, straight, its margins distant. Jaw, according to Morse, of S. lineatus,
. Bulletin - United States National Museum. Science. Animal of 77. lineatus, enlarged. (Voise.) Fig. 35. HELICODISCUS, Morse. Animal heliciform; mantle posterior, thin, simple, protected by a shell; other characters as in Patula. Shell discoidal, widely umbilicated, not shining; si)ire concave; whorls 4, equally visible above and below, the last scarcely larger than the rest, not deflected; aperture rounded, vertical; several pairs of tubercles at intervals within, on the inner surface of the outer whorl; peristome simple, straight, its margins distant. Jaw, according to Morse, of S. lineatus, low, wide, crescentic, ends much attenuated, acute; cutting margin with a median, beak-like projection; anterior sur- jaw of H. lineatus. facc without ribs, but covcrcd with striai con- verging obliquely towards the beak-like prominence. Fig. 36 shows the general arrangement of the teeth upon the lingual Fig. 36. membrane. The characters I of the separate teeth are better shown in Plate IV lof T. M., V, Fig. M. Morse ^ gives 77 rows of 12-1-12 Lingual dentition of if. ii/ieatws. (ilorse.) teeth Cach witll 4 PCrfcct laterals. Leidy, in T. M., Vol. IT, 262, Fig. gives 13-1-13 teeth, with 5 i)erfect laterals. The membrane examined by me has 12-1-12 teeth, with 4 perfect laterals. The central teeth have a base of attachment very small, longer than wide, with expanded lower angles and reflected upper margin. Ketiection very small, with a stout, short median cusp, and very short, blunt side cusps, all the cusps with short cutting points. The lateral teeth have a base of attachment three times as wide, and somewhat longer than the centrals, and asymmetrical by the suppres- sion of the inner, lower lateral expansion; the upper margin is broadly reflected; the reflection is short but symmetrical, having two equally developed short, stout side cusps, bearing short cutting points; the median cusp is stout, long, extending nearly to the lower edge of the base of attachment, beyond which p
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