. Annals of the Carnegie Museum. Carnegie Museum; Carnegie Museum of Natural History; Natural history. 182 Annals of the Carnegie Museum. Raphistoma immaturum (Billings). Pleurotomaria immatura Billings, 1859, Canadian Naturalist - and Geologist, Vol. IV, p. 454. Although this species has never before been figured, it may easily be recognized from Billings' description, as it is the only species of Raphistoma in the Chazy with step-like whorls. In Raphistoma stamineum and Raphistoma striatum, when the central whorls are ele- vated, the outer edge of the body whorl is also usually elevated so t
. Annals of the Carnegie Museum. Carnegie Museum; Carnegie Museum of Natural History; Natural history. 182 Annals of the Carnegie Museum. Raphistoma immaturum (Billings). Pleurotomaria immatura Billings, 1859, Canadian Naturalist - and Geologist, Vol. IV, p. 454. Although this species has never before been figured, it may easily be recognized from Billings' description, as it is the only species of Raphistoma in the Chazy with step-like whorls. In Raphistoma stamineum and Raphistoma striatum, when the central whorls are ele- vated, the outer edge of the body whorl is also usually elevated so that the outer whorl gives the whole shell a somewhat concave border. In Raphistoma immaturum, each whorl is a little higher than the preceding, making steps up to the apex (figure 2) and at the same time the top of each whorl slopes up toward the apex, so that the surface is like that of Lio- spiraamericana (Billings) of the Black River. In all the specimens seen, the lower part of Raphistoma immaturum is less prolonged and ventricose than in Raphistoma striatum and Raphis- toma stamineum, and the whole shell is more like the Black River and the Trenton forms of Liospira. Description (Figure 2). Shell small, consisting of five or six whorls, each a little above the one outside it. The apex is always ele- vated and the slope is regular from the apex to the outer margin of the body whorl. The lower portion of the body whorl is rounded, but is not so conical as in Raphistoma stami- neum. The angle at the margin is acute. The section of the outer whorl is almost a parallelogram, rather wide, gently convex in the outer lip and base, and straight on the top. The umbilicus is closed in adult testiferous shells, and small in young shells with test. The surface markings show numerous fine growth lines which bend sharply backward from the suture, are interrupted by a raised line on the middle of the top of the whorl, curve a little forward, then back. Fig. 2. Raphistoma immaturum Billing
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