PALEONTOLOGY. 151 



found in rare cases in the Hamilton group, at Broadwell's mills, on 

 Thunder Bay River, while in the corniferous limestone of Canada, 

 and at the Falls of the Ohio, it is quite common. 



Plate LIII., Lower tier. — The six specimens in two vertical rows 

 on the left side of the plate, and the lower one in the central 

 row. The middle specimen in the second row is a calcified speci- 

 men from Mackinac ; the next specimen below and the one in the 

 central row are specimens from Crab Orchard, Kentucky. Of the 

 remainder of the group, the two large specimens are found in the 

 drift of Ann Arbor ; the two smaller ones are from the Falls of 

 the Ohio. 



ZAPHRENTIS UNGULA, N. Sp. 



Conical, transversely compressed, and, in the direction of the 

 compression, curved polyp cells, more flattened on the convex 

 side of the curvature than on the opposite. Surface annulated by 

 linear constrictions, with intermediate, broad, rounded rugae ; apex 

 of polyparia pointed. Calyces moderately deep, gently expanded 

 near the margins, gradually narrowing into an obtuse, transverse, 

 central pit, which is joined by a septal fovea, situated in the me- 

 dian line of the flattened broader side. Lamellae stout, subequal 

 near the margins, but alternately long and short ; the longer ones 

 extend nearly to the centre ; the bottom of the small central pit is 

 usually free of crests. Dimensions of polyparia from two to three 

 centimeters in transverse calyx diameter by a little more than half 

 that measure in the opposite direction, and in length exceeding the 

 greater width by about one fourth. Number of lamellae in medium- 

 sized specimens, about 90 ; in larger ones, 100. Found in the upper 

 Helderberg group, at the Falls of the Ohio, and rarely in the 

 drift of Michigan in silicified condition. 



Plate LIIL, Lower tier. — The two right-hand specimens; the 

 lower one is about the largest size found. 



ZAPHRENTIS COMPRESSA, N. Sp. 



Conical compressed polyp cells, straight, or curved in the direc- 

 tion of the narrow side. Large specimens have a calyx diameter 

 of about eight centimeters in one direction, and four in the other, 



