. The Canadian naturalist and geologist. Natural history -- Periodicals. Fig . IT. /^ff^'^ro â â ^ ^B^sii* -\ "^ Fig. 20. Fig. 18. Fig. Fig. 21. Figs. 22 and 23. Figs. 17,18, and 19.âAtrijpa plena. Figs. 20, 21, 22, and 23.âAtrypa hemipUcata. Airy pa hemipUcata is easily recognised by its smoothness in the upper part, and by the broad folds below, which extend only half way to the beaks. This fossil is somewhat pentagonal, wider than long, and generally rather flat than globose. The sinus as well as the broad plications extend only half the length, and the surface is sometimes marked
. The Canadian naturalist and geologist. Natural history -- Periodicals. Fig . IT. /^ff^'^ro â â ^ ^B^sii* -\ "^ Fig. 20. Fig. 18. Fig. Fig. 21. Figs. 22 and 23. Figs. 17,18, and 19.âAtrijpa plena. Figs. 20, 21, 22, and 23.âAtrypa hemipUcata. Airy pa hemipUcata is easily recognised by its smoothness in the upper part, and by the broad folds below, which extend only half way to the beaks. This fossil is somewhat pentagonal, wider than long, and generally rather flat than globose. The sinus as well as the broad plications extend only half the length, and the surface is sometimes marked " by fine, concentric, filiform, subimbricating lines, which are more conspicuous towards the base of the shell, and beautifully undulated in crossing the ; The beaks are very short, and about equally incurved. It is rather common in the Trenton limestone, but not so abundant as J. increbescens. The specific means simply half-plicated. Professor Hall gays :â" This peculiar and beautiful species is rarely found in western localities, but is nevertheless extensively distributed in Xew Tork. It is readily distinguished by its usually rotund figure, and short prominent plications in the lower half of the shell, while it is smooth above, or only marked by fine concentric lines. The sinus at the base usually occupies one fifth of the cu-cumference of the shell, which, with the basal and cardinal slopes, give it a pentagonal appearance. In many specimens collected from the crystalline limestone, I have been able to observe only the plications on the mesial portion, while in the softer or shaly limestone, the lateral ones have all the distinctness of those presented in the tigureSi" Palaeontology of New York, Vol. 1, Page Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Natu
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