442 PALEONTOLOGY OF NEW YORK. 



In form, this shell is very like the preceding, but uniformly smaller in size 

 and marked by more or less distinct, angular concentric ridges. The variation 

 of form, and surface characters, is illustrated in the figures cited on plate Ixxii. 



It also resembles Ludna lineata, Goldfuss (Pet. Germ., p. 226, pl. 146, fig. 8), 

 from the Devonian of the Eifel, and may not be specifically distinct. 



Formations and localities. Very abundant in the shales of the Hamilton group, 

 in the ejistern and central parts of New York, and in the cherty layers above 

 the Hydraulic beds at the falls of the Ohio, and in Clarke county, Ind. 



Paracyclas Ohioensis. 



r 



PLATE LXXU, FIG. 1 ; and PLATE XCV, FIG. M. 



Lucina {Paracyclas) Ohioensis, Mbbk. Pi-oc. Acad. Nat. Sci., Phila., p. 6. 1871. 



" " " " Pal. Ohio, vol. ii, p. 199, pl. 18, figs, la, b. 1873. 



In pai"t Parcurydas lirata (Cokkad), Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations: Pl. 72, 



figs. 1-19. 



This species is a smaller and more delicate form than P. lirata, and with 

 much finer concentric striae ; the anterior end is more produced and flattened 

 than in either of the preceding species, and the posterior depression, caused by 

 the ligamental groove, is more oblique and more decidedly marked on the exte- 

 rior of the shell. 



The posterior extension, as shown by Mr. Meek, is exaggerated in the origi- 

 nal figures, giving the aspect of an appendage or extension on the posterior 

 side, while it is only that part of the post-cardinal slope above the ligamental 

 groove. Fig. 7b {loc. cit.) well represents the form of the species. A compar- 

 ison of several specimens of this species, with a large collection of P. lirata, 

 shows it to be a very distinct form. 



Formation and localities. The original specimens were derived from Dublin, 

 Ohio. The specimens which have come under our observation are from cherty 

 beds above the Corniferous limestone at the falls of the Ohio and in Clarke 

 county, Ind. 



