PALEONTOLOGY. 453 



the Erie shale at Leroy, Lake county, Ohio. The shell shows it to have 

 been circular, nearly discoid in form, with the surface covered by distant 

 elevated lides or ridges, and corresponds in all respects, as far as can be 

 seen on the specimen, to those from the Marcellus shale and Hamilton 

 beds of New York. 



Genus ORTHIS Dalman. 

 Orthis tioga. 

 Peate VIII, fig. 3. 

 Orthis tioga Hall, Pal. N. Y., vol. 4, p. 59, pi. 8, figs. 20-29. 



Among the concretionary nodules of the Erie shale from Leroy, 

 Lake county, there is one which contains impressions, or casts, of sev- 

 eral valves of the above named species. The specimens are some- 

 what smaller than the general run of the New York Chemung 

 specimens, but otherwise cannot be distinguished from them. The 

 most entire ones are dorsal valves, and are moderately convex, with a 

 decided mesial sinus. The form is transversely oval or elliptical, with a 

 short cardinal area and small depressed beak; the striae are rather coarse, 

 frequently bifurcated and much recurved on the cardinal margins and 

 slopes, many of them running off on the cardinal border. Muscular 

 scars large and sub-flabellate, all the features being the same as the typi- 

 cal forms of the species, modified only in size. 



Genus PAL^ONEILO H. and W. 



Preliminary Notice of Lamellib. Shells of the Upper Held., Hamilton and Che- 

 mung groups, etc., N. Y. State Cab. Nat. Hist, Dec, 1869, p. 6. 



Palceoneilo similis. 

 Plate VIII, figs. 4 and 5. 

 Palceoneilo similis Whitf., Ann. N. Y. Acad. Sci., 1882, p. 217. 



Shell oblong, with nearly equally rounded extremities, and almost parallel 

 dorsal and ventral margins. Anterior end short, a little narrower than the body of 

 the shell, resulting from the constriction below the beaks. Posterior end rounded 

 with a slight oblique truncation below the middle of the height, corresponding tu 

 the very shallow umbonal sulcus of the valves. Beaks situated within the anterior 

 third of the length of the shell, small and unrolled. Valves ventricose, most prom- 

 inent just below the umboneSj and slightly sulcated along the posterior slope. 

 The surface of the shell, so far as can be determined from the matrix, has been 

 smooth or without visible markings. On the internal cast, the condition in which 

 specimens are found, the muscular imprints are faintly marked— the pedal muscles 

 being the most distinct. 



The species is closely related to P. (Leda) Barrisi White and Whitf., 

 Proc. Bost. Soc. Nat. Hist., vol. 8, p. 298 {Palczoneilo Barrisi (W. and 

 W.), H. & W., Prelim. Notice of Lam. Shells of the Up. Held., Ham- 

 ilton and Chemung groups, etc.), but has been somewhat more nearly 

 parallel on the margins, and has a smoother shell. 



Formation and Locality. — In calcareous concretions of the Erie shale, 

 at Leroy, Lake county, Ohio, accompanying the fossil entomostracan 

 from the same locality (next described.) 



