. The Geology of Minnesota . d Worthen sp., Coal Measures, La Salle, Illinois, a, Sideview of an entire specimen of H. planibasalis, x2, showing general form of shell, the flat base, surface GASTROPODA. 1081 Appendix.] markings, apertural slit and band. Tlie line beneath the figure shows the form of the basal side of b, The band of the second to the last whorl of same specimen, with a small portion of thesurface above and beneath it, X3. c, Portion of the flat under surface of another specimen of JS. plani-basalis, x2, showing the direction of the lines of growth and the revo
. The Geology of Minnesota . d Worthen sp., Coal Measures, La Salle, Illinois, a, Sideview of an entire specimen of H. planibasalis, x2, showing general form of shell, the flat base, surface GASTROPODA. 1081 Appendix.] markings, apertural slit and band. Tlie line beneath the figure shows the form of the basal side of b, The band of the second to the last whorl of same specimen, with a small portion of thesurface above and beneath it, X3. c, Portion of the flat under surface of another specimen of JS. plani-basalis, x2, showing the direction of the lines of growth and the revolving lines which cover nearly thewhole of this surface, d, Similar portion of the under surface of E. turbiniformis, x2, showing very delicatelines of growth but no revolving lines, e, Small portion of slope of spire of same for comparison with fig surface markings are appreciably different and the sculpture and section of the slit-band widely atvariance in the two species. (This cut should have appeared on page 956.). Fig. 12.—Several Carboniferous species of Treposptra. a and b, Two views of a perfect specimen ofT. sphcerulata Conrad sp., showing the depressed apex, short slit, projecting upper lip and other featurescharacterizing in part this genus and species, c, Inner whorls of another specimen of this species, xio, show-ing sevciral changes which take place in the early development of the shell. Both specimens are from Spring-field, Illinois, d and e, A small specimen of 1. convcxa Ulrich, natural size and magnified, viewed so as toshow thedepth of the apertural sinus and slit and the depressed convex spire. /, The same specimen viewedfrom above, g, Another specimen, also x2, showing the under side. T. convexaia a new species, differingfrom the others in the gentle convexity of the upper side of the whorls. It is from the Lower Coal Meas-ures at Seville, Illinois, h, Lateral view, X2, of a specimen of T. illinoisensis Worthen sp., from Peoria, Illi-nois. {This cu
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