34 SIXTEENTH REPORT ON THE CABINET OF NAT. HISTORT. 



*' ORTHIS MITIS (n.s.)." 



Shell suborbicular, of moderate convexity ; area about half the 

 width of the shell ; length and width about as four to five ; 

 cardinal extremities rounded. 



Surface somewhat coarsely striated. 



The cast of the ventral valve is depressed-convex above, depressed 

 along the centre below, with a median groove from the adductor 

 scar nearly to the front of the shell. Muscular impression el- 

 liptical, occupying less than half the length of the valve, and 

 about one-third the width : lower half of valve marked by 

 strong vascular impressions. 



Two specimens in the State Collection, having respectively the length of 

 about one-half and five-eighths of an inch, are referred with hesitation to 

 this species. The cast of the ventral valve possesses characters which dis- 

 tinguish it from any species of which I know the interior. It is possible that 

 these may be the young of 0. lima, of which I do not know the interior at 

 this time. 



Geological formation and locality. In the Schoharie grit, in Albany and 

 Schoharie counties. 



'' OETHIS SEMELE ( n. s.)." 



Some imperfect specimens showing the interior of the ventral valve, and 

 also a small specimen of the ventral valve, possess characters approaching 

 very nearly to 0. vanuxemi. From the same locality there have been ob- 

 tained casts of a dorsal valve, which are more elevated in the middle, with 

 the apex more produced that in that species. These casts give indications of 

 a median sinus with an elevation on each side of it, and thence an abrupt 

 slope to the cardinal extremities, and curving to the front and lower lateral 

 margins. 



In this character, they more nearly resemble the dorsal valves of Orthis 

 leucosia; while the muscular impressions of the ventral valves, from the 

 same locality, are broader than in that species. The hinge-line of a ventral 

 valve is three-fifths the greatest width of the shell, which is greater than 

 in either 0. vanuxemi or 0. leucosia, while the striae are also much coarser. 

 This specimen occurring with the others, while no other form of ventral 

 valve has been seen in the same association, indicates the probable relations 

 of the other specimens. 



Although the material in my possession is too imperfect for a complete 

 description, I have indicated the prominent features of the species, in order 

 to call attention to the occurrence of this form in the limestones of the 

 Upper Helderberg group. 



Geological formation and locality. In the Onondaga limestone : near 

 Clarence hollow, Erie county. I have seen a similar form from the limestone 

 near Columbus, Ohio, 



