390 PALAEONTOLOGY OF NEW-YORK. 



Geological fommtion and localities. The original or type specimens of the spe- 

 cies occur in beds of the ago of the ILiniilton group, at Thunder bay, Michigan. 

 It is found in the same horizon at York in Livingston count}% and at Hamburgh 

 on the sliorc of Lake Eric. It has likewise been found at AVatcrloo, Iowa, by Mr. 

 R. P. Whitfield. 



Terebiatula clia (n.s.). 



' PLATE LX. 



Shell ovate, arcuate on the ventral side ; beak prominent. 



Ventral valve regularly arcuate from beak to base, gibbous in the mid- 

 dle and above ; umbo prominent ; beak little incurved and Broadly 

 truncate by a rounded foramen, which is limited on the lower side by 

 two large deltidial pieces. 



Dorsal valve regularly convex, the greatest convexity in the middle, 

 where it is about equal to that of the opposite valve. The depth, width 

 and length are as two, three and four-eighths of an inch. 



Surface concentrically striate, shell-substance punctate. 



Geological formation and locality. This siiccies occurs at Waterloo, Iowa, in 



strata of the age of the Upper Ileklerberg or Hamilton group. Received from Mr. 



O. St. Joux. 



^ Terebratula jucuiida (n. s.). 



PLATE LX. 



Shell subcircular or very broadly ovate, the length and width about 



equal, regularly rounded below and abruptly narrowing above the 



middle. 

 Ventral valve gibbous in the middle, curving regularly to the base and 



baso-lateral margins : beak obtuse, and incurved over the umbo of 



the opposite valve ; apex truncated by a rounded foramen. 

 Dorsal valve rather regularly convex, the greatest convexity a little 



above the middle, curving to the base and baso-lateral margins. 



Length of specimens, a little more than three-eighths of an inch. 



On cutting down from the dorsal side, the loop is visible, showing the 

 terebratuloid character. 



