set PALAEONTOLOGY OF NEW-YORK. 



Lei<>rliynclius j^lobuliforiiiis. 



PLATE LVII. 

 Mrypa globul\formit : VASnxKK, Geol. Report Third Dlst. New-Tork, p. 182, f. 2. 1842, 



I adopt the name applied by Mr. Vanuxem to some gibbous forms of yhat 

 appear to be Leiorhynchus. Tlie species is spoken of as occurring "in myriads " 

 in this group of strata in the Third District. I have nevertheless had an opportu- 

 nity of examining but a few individuals, which are casts of gibbous dorsal 

 valves, marked along the centre by four or five strong rounded plications, whicli 

 are a little elevated above the general surface of the shell, and margined by a 

 narrow elongate muscular impression. It is possible that larger collections may 

 show the propriety of uniting these with L. mesacostalis. 



Geological formation and localities. This siDccies occurs in the Chemung group 

 in the south part of Otsego county, and elsewhere in the southeastern part of the 

 State of New- York. • 



Leiorhynchus dubius (n. s.). 



PLATE LVII. 

 Shell broadly ovate, rapidly expanding in width from about the middle 



of its length, and wider than long ; concave along the cardino-lateral 



margins. 

 Valves moderately and almost equally convex ; the ventral valve scarcely 



sinuate, and the dorsal valve with a slightly elevated fold near the 



front. 

 Surface marked by twenty-four to twenty-six slender rounded plications, 



of which about six are raised on the mesial fold. Length half an inch, 



with the width a little greater. 



Of two well-marked specimens, one has a slight fold and sinus, affec- 

 ting only the front of the shell ; the other specimen is not perceptibly 

 marked by this feature. The plications or striae are finer than in any 

 other species, and extend quite to the apex of the valves. 



This species is apparently from the calcareous beds of the Marcellus shale, but 

 the particular locality is not known. 



