. Annual report of the regents of the university of the state of New York on the condition of the State Cabinet of Natural History and the historical and antiquarian collection annexed thereto. Science. 158 TWENTIETH REPORT ON THE STATE CABINET. While this volume has been going through the press, Mr. R. P. Whit- field has made examinations of the internal appendages of several forms of Atrypa, and has found that the short processes, usually repre- sented near the base of the crura, do actually unite, forming a loop which connects the spires, as shown in the accompanying figure. Atrypa reticula
. Annual report of the regents of the university of the state of New York on the condition of the State Cabinet of Natural History and the historical and antiquarian collection annexed thereto. Science. 158 TWENTIETH REPORT ON THE STATE CABINET. While this volume has been going through the press, Mr. R. P. Whit- field has made examinations of the internal appendages of several forms of Atrypa, and has found that the short processes, usually repre- sented near the base of the crura, do actually unite, forming a loop which connects the spires, as shown in the accompanying figure. Atrypa From collections made in Iowa during the geological survey, and from others more recently made, in different places in that State, by Mr. R. P. Whitfield, at points more than a thousand miles west of New-York, we learn that in all localities the distinction between Atrypa reticularis, or its representative, and the associated species, is more strongly marked than in the eastern collections, and there is nowhere any indication of a gradation from the one to the other. At Waterloo, in beds which are apparently of the age of the Upper Helderberg group, there occurs a form with distinct narrow plications, a regularly convex dorsal valve, and a flat or concave ventral valve. It is not very unlike a strongly plicated form from Refrath in Germany, or approaching A. insquamosa of Schnur. At Independence and Waverly the specimens resemble the finely plicate Atrypa prisca from Refrath, with the margins compressed, the dorsal valve very convex, and the ventral valve flattened or concave towards the margin. They have very conspicuous concentric lamellae. Some of the specimens are two and a half inches in diameter, and the volutions of the internal spires vary from twelve to twenty according to the age of the shell. The Atrypa aspera, or its representative, in the beds at Independence and Waverly, has the dorsal valve very gibbous, with the ventral valve nearly flat or concave towards
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Keywords: ., bookcentury1800, bookdecade1850, booksubjectscience, bookyear1853
