. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology; Zoology. STENOTREMA. 291 shorter, tho cuttino; points more produced, and thus gradually the form of the marginal teeth is reached. They are low, wide, the reflection equalling the base of attachment, the cutting points long, oblique, usually two in number, the inner one generally, and the outer one rarely, bluntly bifid: the outer bifurcation of each is more produced than the inner. Tliere is great varia- tion in the denticulation of the marginal teeth even on the same linijual mem- brane. A transition from laterals t
. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology; Zoology. STENOTREMA. 291 shorter, tho cuttino; points more produced, and thus gradually the form of the marginal teeth is reached. They are low, wide, the reflection equalling the base of attachment, the cutting points long, oblique, usually two in number, the inner one generally, and the outer one rarely, bluntly bifid: the outer bifurcation of each is more produced than the inner. Tliere is great varia- tion in the denticulation of the marginal teeth even on the same linijual mem- brane. A transition from laterals to marginals similar to that of S. spinosum is found in 5. barbigerum, labrosum, Edvardsi, stenotremum, hirsutum, germanum, and monodon. There seems no difference in the characters of the teeth of the different species examined by me, excepting the slight one of the greater or lesser devel- opment of the side cusps of centrals or laterals, especially the former; whether this is constant can only be proved by a careful examination of every portion of each lingual. In S. hirsutum I found these cusps more developed than in the other species. Stenotrema spinosum, Lea. VoL III. PI. XLIV. Fig. 1. Shell imperforate, lenticular, with the upper surface much flattened, acutely carinated; epidermis dark chestnut-color, with minute, hair-like processes lying flat upon the whorls in the direction of their lines of growth, striate ; whorls 6, of nearly uniform width, and decreasing very ^^S- 189. gradually from the aperture to the spire ; suture distinct, slightly raised ; aperture very narrow ; peristome yellowish-white, near its junction with the body-whorl thickened, angulated, and slightly reflected, with a median cleft : parietal wall with a lone:, yel- * '=' '' iS. spinosum. lowish, narrow, projecting tooth, extending from the umbilical axis to the angle of the peristome, and parallel with its thickened edge; base convex, with the umbilical region slightly indented ; within the shell, s
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