. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology. POLYGYRELLA. 289 Fig. Jaw of. P. polygyrella. POLYGYRELLA, Bland. Animal heliciform ; mantle subcentral; other characters as in Patula. Shell widely umbilicated, discoidal, ribbed above, smoother below; whorls 7-8, gradually increasing, the last deflected above, furnished within with two rows of three teeth; base flattened, umbilicus of equal size to the apex; aperture subver- tical, oblique, lunate-oval; peristome white, simple, much thickened within, margins joined by a white, pliciform, elevated, triangular t
. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology. POLYGYRELLA. 289 Fig. Jaw of. P. polygyrella. POLYGYRELLA, Bland. Animal heliciform ; mantle subcentral; other characters as in Patula. Shell widely umbilicated, discoidal, ribbed above, smoother below; whorls 7-8, gradually increasing, the last deflected above, furnished within with two rows of three teeth; base flattened, umbilicus of equal size to the apex; aperture subver- tical, oblique, lunate-oval; peristome white, simple, much thickened within, margins joined by a white, pliciform, elevated, triangular tooth. Central Province ; a single species known. Jaw of the only known species, P. polygyrella, very low, wide, very slightly arcuate, ends very gradually attenuated: cutting margin without median pro- jection : anterior surface with numerous (even 26), broad, slightly separated ribs, denticulating either margin. Lingual membrane (PL VII. Fig. A) long and narrow. Teeth 27—1—27, with 5 perfect laterals. Centrals subquadrate, the lower lateral angles but little expanded; the upper margin broadly reflected: reflection large, wide, with distinct, but small, rounded side cusps bearing short conical cutting points, and a very stout median cusp reaching the lower margin of the base of attach- ment, beyond which projects the short, stout, conical cutting point. Laterals like the centrals, but asymmetrical by the suppression of the inner, lower angle of the base of attachment, and the inner side cusp and cutting point. First marginals a simple modification of the laterals by the lesser development of the cutting point (b). Outer marginals (c) low, wide, the reflection equal- ling the base of attachment and bearing one inner, short, stout, oblique cutting point, and two shorter outer blunt cutting points. Polygyrella is quite distinct from all the other American genera by the form of its jaw and the large number of ribs upon its anterior surface. Fig. 187. Polygyrella polygyrella, Bl
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Keywords: ., bookauthorha, bookcentury1800, bookdecade1870, booksubjectzoology
