362 
PALAEONTOLOGY OF NEW-YORK. 
In some of its phases, this species approaches to the Leiorhynchus multicosta ; 
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, Spirifera mucronata, a species of Athyris 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. 
Leiorhynchus sinuatus (n. s ). 
PLATE LVII. 
Compare Leiorhynchus limitaris (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 strise as in others of the genus. 
It may be found that this form is only a variety of L. limitaris , existing under 
other conditions and at a later epoch. The plications are coarser, and do not 
extend to the beak as in L. limitaris , 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 places in Southern 
New-York. 
Leioiliynclms mesacostalis. 
PLATE LVII. 
Mrypa mesacostalis : Hall, Geol. Report Fourth Dist. New-York. Illustrations of Fossils of the 
Chemung group, 64, f. 1 a and 1 b. 1843. 
Leiorhynchus mesacostalis : Id., ThirteenthReport on the State Cabinet, p. 86. 1860. 
Shell oval or ovate, more or less gibbous, sinuate towards the front. 
