FOSSILS OF THE SILURIAN AND DEVONIAN ROCKS. a I 



the center line of the deflecting branch, and the other about one-fourth of 

 an inch above it, which appear to be the buds of two new branches, but 

 whose positions make it somewhat doubtful, inasmuch as those new stems 

 would leave the plane of the two existing prongs. In similar species, as 

 P. ramosa and P. briareus, the branches start always from the sharp edge, 

 and I do not doubt that the same is the case with P. hilli. We may, 

 therefore, assume, that very few branches are formed. This species is gen- 

 erally found in more or less straight, thin strips, of different width, the 

 cross sections of which are either acutely elliptical or elliptic-lanceolate. Both 

 sides are entirely equal; they are most convex in their central line, from where 

 they slope in a regular but gentle curve to the lateral margins, where the sur- 

 faces of both sides meet at a very acute angle. The surfaces of both sides are 

 covered by transverse, sharply angular ridges, with interspaces of about twice 

 their own width. Some of these plications cross the branches from one edge 

 to the other in a straight line, rectangular with the margin, the course of 

 others is somewhat oblique, and others again cross the surface only partly. 

 These shorter ribs are always intercalated, and never produced by bifurcation. 

 The whole zoarium is covered by closely arranged rhomboidal cells of about 

 equal size, the walls of which form nearly straight lines, crossing each other 

 obliquely. The largest specimen in my possession measures nearly four 

 inches in length, -by more than an inch in width ; in its whole extent it does 

 not show any branch ; it has thirteen transverse ribs in the space of an inch. 

 A smaller specimen measures one inch and three- eighths in length, by one- 

 fourth of an inch in width, with nineteen cross ribs in the space of an inch. 



Formation and Locality. This species is named after Dr. O. O. Hill, formerly of Cincinnati, Ohio, 

 who first discovered it. It was afterwards found rather abundantly in the upper strata of the Hudson 

 Kiver group at Danville, Ky., by Prof. Linney, of the Kentucky Geological Survey. 



MOLLUSCA. 

 BRACHIOPODA. 

 Genus Crania. Ketzi U8 . 



Crania. Ketzius. Schrift der Berliner Gesellschaffc Nat. Freunde. 1781. Etymology: Kranion 



the upper part of the skull. 



Shell smooth or -striated by radiating striae ; umbo of the dorsal valve sub- 

 central ; umbo of the ventral valve sub-central, marginal or prominent and 

 cap-like, with an obscure triangular area traversed by a central line. Shell 

 usually attached to other shells or marine bodies. The large muscular impres,- 



