Description of Twelve New Fossil Species. Ill 



the plates of the dome, is covered by an arch composed of minute plates. 

 The length of an arch is about 4^ lines, width 3 lines, and eleva- 

 tion 1^ lines. This arch, extending from the dome to the furrow upon 

 the inner side of the arm (if not farther), is a striking peculiarity-. 



The specimen illustrated and described was found in the Hudson 

 River Group, at Cincinnati, and is from the collection of 0. B. Dyer, 

 Esq. 



This species was described and illustrated, b}'^ Sidue}' S. L^'on, in 

 18G9, in the Trans. Am. Phil. Soc, vol. 13, under the name of Atax- 

 ocrinas caponiformis. His specimen was somewhat crushed, and 

 hence his illustrations do not show several peculiarities, which are 

 presented, in our illustrations. 



In the proceedings of the Acad. Nat. Sci. Phil., in 1865, Meek and 

 Worthen proposed the name Anomalocrinus as a subgenus, but did 

 not clearly define the generic characters. In the Illinois Geo. Sur., vol. 

 3, in 1868, however, they more particularly described the subgenus, 

 and illustrated the species, A. incurvus. The diagrammatical showing 

 of the structure is very erroneous, which may have misled Prof. Lyon, 

 but the description is sufficiently clear to give Anomalocrinus priority 

 over Ataxocrinus. 



In 1873 (Geo. Sur. of Ohio, pt. 2, Palaeontology ), Prof. Meek re- 

 described the Anomalocrinus incurvus, and illustrated it from a speci- 

 men in my collection, and took the position, thiit Ataxocrinus caponi- 

 formis is the same crinoid, and therefore a synonym. I followed him, 

 in classing the latter as a synonym, in the " American Palaeozoic 

 Fossils," in 1877. But this was, certainly, error, and I am glad that 

 I have the opportunity of restoring the name caponiformis.^ to a spe- 

 cies, so distinct, from incurvus, if we regard the specimen illustrated, 

 in the Ohio Palaeontology, as a type. 



Let us look at some of the differences. The incurvus has six basal 

 plates, the sixth plate being quadrangular and below the right ante- 

 rior first radial. This radial rests upon three basal pieces instead of 

 two. This is an essential difference, but we need not stop here, for 

 the general form ot the body and proportion of the plates are very 

 different in the two species: The body of the caponiformis forms a 

 broad almost flat disk, while the incurvus has a moderately deep cup and 

 expands on the azygos side, only about a line be^-ond the perpendicu- 

 lar, with the column. The measurements of ihe two specimens are 

 as follows:* 



* lu this measurement I follow Meek in calling the azygos side the posterior side, 

 in order to make the comparison with his measurement clear, though in the descrip- 

 tion the azygos side is treated as the anterior side. 



