. Bulletin - United States National Museum. Science. 346 A MANUAL OF AMERICAN LAND SHELLS. Jaw abseut. Lingual membrane narrow, with chevron-shaped rows of uuiform, aculeate, separated teeth; central tooth with a long, slender, straight base of attachment, with incurved sides and with inferior, lateral, sliglitly expanded angles, and with the upper margin reflected and extended into a long, slender, acutely pointed cusp. There are no lateral teeth, the balance of the membrane being composed of marginal teeth of the pure aculeate form. Each row of teeth on either side of the median line curves
. Bulletin - United States National Museum. Science. 346 A MANUAL OF AMERICAN LAND SHELLS. Jaw abseut. Lingual membrane narrow, with chevron-shaped rows of uuiform, aculeate, separated teeth; central tooth with a long, slender, straight base of attachment, with incurved sides and with inferior, lateral, sliglitly expanded angles, and with the upper margin reflected and extended into a long, slender, acutely pointed cusp. There are no lateral teeth, the balance of the membrane being composed of marginal teeth of the pure aculeate form. Each row of teeth on either side of the median line curves first backward, with the teeth rapidly increas- ing in size as they pass outwards, and then forwards as the teeth grad- ually again become smaller, giving an irregularly cresceutic shape to the half-row of teeth. This is shown particularly in Gl. Albersi and G. rosettj less so in GI. truncata. The central tooth was overlooked by Wyman, Lei«ly, and other of the earlier investigators. It has since been detected in GI. truncata, rosea, algira, Sowerbyana, pUcatula, fusi- form is, Albersi ; in semitarum, PhilHpsi, of the subgenus Varicella; also ,solidula, of subgenus Oleacina. This central tooth is rather difficult to istudy, being on a different plane from the other teeth and apparently much less developed. Its cusp is generally simple, long, and narrow; but in G. rosea it has a decided blunt cutting point, and in G. semitarum it has a long, slender cutting point; for that of G. truncata see be- low. The side teeth are all of the purely aculeate type; the base of attach- ment is long, narrow, incurved at sides, gradually rounded above, ex- panded and bluntly truncated below, the general outline being some- what like that of the sole of a shoe. From this base of attachment S!)rings a large, aculeate cutting point. These side teeth are like the marginals in Zonites, Limax, &c. ; they may therefore be called mar- ginal teeth, and the lateral teeth, usually present intho, Liniac
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