444 GEOLOGY OF OHIO. 



Genus SPIRIFKRA Sowerby. 



Spirifera Maia. 



Plate VII, fig. 14. 

 Athyris Maia Billings, Can, Jour. Ind. Sci. and Arts, May, 1860, p. 276. 

 Sperifera Maia (Bill.) Hall, Pal. N. Y. vol. 4, pt. 1, p. 416, pi. 63, figs. 6-13. 



Several single valves of this species have been obtained from the 

 thin-bedded limestones, associated with the Discina and Leiorhynchus 

 bearing shales, on W. Meeteer's farm, two and a half miles south of Dub- 

 lin, Ohio; but in too imperfect a condition for illustration; still, how- 

 ever, sufficiently distinct to leave no reasonable doubt of their identity. 

 They are smaller in size than those from the Upper Helderberg limestone 

 of Canada, but otherwise not different so far as can be discovered from 



the imperfect material on' hand. 



> 



Genus LEIORHYNCHUS Hall. 



Leiorhynchus iiviitaris. 



Plate VII, fig. 11. 

 Orthis limitaris Vanuxm, Geol. Rept. 3d Dist. N. Y., 1842, p. 146, fig. 3. 

 Atry pa limitaris Hall, Geol. Rept. 4th Dist. N. Y., 1843, p. 182, fig. 11. 

 Leiorhy?ichus limitaris Hall, 13th Rept. State Cab., p. 85, 1860. 

 Leiorhynchus limitaris Hall, Pal. N. Y. vol. 4, p. 356, pi. 56, figs. 6-21. 



Shell small in size, seldom exceeding five-eighths of an inch in width and usu- 

 ally not more than three-eighths ; form orbicular in outline and lenticular in pro- 

 file when not compressed. Valves subequal in depth and rotundity, the ventral 

 beak slightly extending beyond that of the dorsal and the middle third or more of 

 the width of the valve depressed, forming a broad but shallow sinus which extends 

 to within a short distance of the beak. Dorsal valve elevated in the middle to form 

 the fold which corresponds to the sinus of the ventral, but which does not continue 

 much beyond the middle of the valve. Surface of the shell marked by from ten to 

 twelve or more low, angular plications, four or five of which are seen in the sinus of the 

 ventral, and a corresponding number elevated on the fold of the dorsal valve, and 

 from three to four or even five marks each side of the shell beyond the limit of the 

 fold and sinus. The specimens are usually marked also by several strong concen- 

 tric lines of growth which form strong varices on the larger specimens, and the 

 plications are not unfrequently divided by slighter depressions along their surfaces, 

 which gives the appearance of being bifurcated, and the plications themselves are 

 very unequal in strength and seldom extend entirely to the apex of the valves. 



This shell is a very well-marked species and cannot well be mistaken 

 for any other of the several species, which, so far as is yet known, are 

 limited to certain horizons; this one characterizing the horizon of the 

 Marcellus shale in New York, wherever the species has been found. Its 

 occurrence in Ohio has not heretofore been known or suspected, and its 

 presence in numbers, flattened and compressed in a dark brown, some- 

 what fossil shale, presenting so exactly the characters and appearance 

 that it does in the shales of New York, and also associated with other 

 characteristic forms of the Marcellus shale, is a somewhat significant 

 fact, and one of considerable importance in its stratigraphical relations. 



