. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology; Zoology. TRIODOPSIS. 301. Fig. 196. Jaw of T. appressa. TRIODOPSIS, Raf. Animal hclicifonn, nianllo posterior, other characters as in Pnfula, q. v. Shell imperforate or umbilicated, orbicularly depressed or sub^lohose; more or less obliquely striated; whorls ^'8- ^^^- 5-7, the last somewhat deflexed in front; aperture sinuously coarctate, su])triangular; peristome white, thickened, broadly and angularly reflexed, usually dentate; parietal wall of the aperture with a strong. Animal of T. palliata. obliquely entering de
. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology; Zoology. TRIODOPSIS. 301. Fig. 196. Jaw of T. appressa. TRIODOPSIS, Raf. Animal hclicifonn, nianllo posterior, other characters as in Pnfula, q. v. Shell imperforate or umbilicated, orbicularly depressed or sub^lohose; more or less obliquely striated; whorls ^'8- ^^^- 5-7, the last somewhat deflexed in front; aperture sinuously coarctate, su])triangular; peristome white, thickened, broadly and angularly reflexed, usually dentate; parietal wall of the aperture with a strong. Animal of T. palliata. obliquely entering denticle. The subgenus inhabits almost exclusively North America, especially the Eastern Province. Two Central American species have, however, been described, and one European species, personata, Lam. This last is said by Moquin-Tandon to have 3-5 separated ribs upon its jaw, while our American species, as shown above, have numerous ribs. Jaw stout, arcuate, low, wide, ends but little attenuated, blunt; cutting margin without median projection; anterior surface with numerous decided, separated ribs, denticulating either margin. There are about 15 in palliata; 10 in ohstricta; 15 in appressa; J 4 in injiecta; 10 in Rugeli; 14 in fallax; over 10 in Hopeto- nensis; 17 in Van Nostrandi; 14 in introferens; over 12 in Harfordiana vultu- osa; 11 in loiicata;^ over 10 in (ridentata. I have not examined //. Mullani?' Triodopsis does not differ from Mesodon or Polygyra in the character of its jaw. Stenotrema, on the other hand, is readily distinguished by having the ribs broader and more crowded on its jaw. The general arransement of the teeth on the lingual membrane is as in Patula. The characters of the individual teeth are given on Plate VII. I have selected appressa (PI. VII. Fig. Q) to show these characters, comparing the dentition of the other species with it. The centrals are longer than wide ; the base of attachment has its outer, lower, lateral expansion but little developed, its
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