58 



FALJEONTOLOQY OS NEW-TOEK- 



Position and locality. Nearly all the specimens were found in the lower green shale at 

 Sodus, Wayne county. A few individuals of the smaller forms have been found at Rochester ; 

 but in the western extension of the group, none have been observed. (State Collection.) 



441. 23. ORTHIS TRINUCLEUS (71. sp.). 



Pl. XX. Fig. 8 a, b, c. 



Suboval, longer than wide ; interior of ventral valve concave, presenting a strong longitu- 

 dinal ridge and three strong obtuse teeth at the hinge. 



The only specimens (except very imperfect ones) which I have seen, are the interior of the 

 ventral valve and a cast of the same. The interior is smooth, with the prominent ridge noticed, 

 and three conspicuous teeth in the hinge, which, with its rather elongated form, distinguish it 

 from any other species. 



Fig. 8 a. Interior of ventral valve. 

 Fig. 8 b. Cast of ventral valve. 

 Fig. 8 c. The same magnified. 



Position and locality. In the impure iron ore bed at Cental's mill, Wayne county, 



442. 24. ORTHIS TENUIDENS {n. sp.). 



Pl. XX. Tig. 9 a- e. 



Ventral valve nearly flat, with a depression along the centre, and becoming slightly convex 

 above the centre ; hinge-line nearly or quite as long as the width of the shell ; surface finely 

 striated ; striee somewhat in fascicles ; hinge showing three small thin teeth, which are closely 

 approximate, middle one very short ; muscular impression obovate or obcordate. 



This valve resembles the ventral valve of O. elegantula ; but the hinge-line is proportionally 

 longer, the teeth smaller and closer together, and the muscular impression of different form. 



The form of this shell, and its general appearance, are much like Lept^na ; but it appears, 

 however, to be a true Orthis. 



Associated with the ventral valves, which are preserved mostly as casts, are impressions of 

 a very convex dorsal valve, which, probably, is of the same species. 



Fig. 9 a. Ventral valve with the shell partially removed. 



Fig. 9 J. A more perfect cast, showing the form of the muscular impression. 



Fig. 9 c. The last enlarged. 



Fig. 9 d. The impression of a dorsal valve. 



Fig. 9 e. The last enlarged. 



Position and locality. This species occurs in considerable numbers in an iron-stained shaly 

 sandstone, and also in semi-calcareous layers, on the road from New-Hartford to Clinton vil- 

 lage, Oneida county, ( state Collection.) 



