363 PALAEONTOLOGY OF NEW-YORK. 



In some of its phases, this species approaches to the Jjeiorhynckus muHt'costa ; 

 but it is proportionally broader, and the plications do not extend so far towards 

 the beak, while the prevailing aspect is quite different. 



Geological formation and locality. Specimens of this species were collected 

 in the northern part of Ohio, from a calcareous rock, associated with Stropho- 

 donta demissa, S. perplana, Spin/era mucronata, a species of Athyns and a Meris- 

 tella, by Dr. G. M. Kellogg of Keokuk, Iowa, from whom I have received them. 



I have the cast of a single specimen from the Hamilton group in Eastern New- 

 York, which very closely resembles this one, and is probably identical with it. 



Leiorh} nclius sinuatus ( n. s.). 



PLATE LVIL 

 Compare Leiorhynchut limitarit (ut sup.). 



Shell ovate or orbicular, more or less distinctly sinuate from the mesial 

 sinus, and truncate in front. 



Ventral valve moderately convex, with the sides nearly flat, depressed 

 in the middle and extending into a broad shallow sinus. 



Dorsal valve moderately convex and sometimes gibbous, gently curving 

 to the sides ; the mesial fold broad and flat. 



Surface marked by about twelve to fourteen or fifteen rather coarse 

 rounded or subangular plications, of which four or five are depressed 

 in the mesial sinus. The sinus and fold are not often conspicuous above 

 the middle of the shell. Concentric strieB as in others of the genus. 



It may be found that this form is only a variety of L. limitans, existing under 

 other conditions and at a later epoch. The plications are coarser, and do not 

 extend to the beak as in L. limitans, and the shell attains a somewhat greater size 

 and more robust aspect. , 



Geological formation and localities. This species occurs in the shales of the 

 Chemung group at Ithaca ; at Chemung narrows, and other phices in Southern 

 New- York. 



Leiorhynclius niesacostalis. 



PLATB LVII. 



Mrypa muacottaUt : Hall, Geol. Report Fourth Diet. New-York. lUnitrations of Fossils of the 



Chomung group, 61, f . 1 a and 1 b. 18-18. 



Ltu>rhyncha$ maacoitalU : Id., ThirtecnthReport on the State Cabinet, p. 80. 18G0. 



Shell oval or ovate, more or less gibbous, sinuate towards the front. 



