134 LOWER PENINSULA. 



circumscribing irregularly polygonal spaces. Radial plications from 

 thirty to forty, linear, crest-like in the circumference of the inner 

 pits, and uniting in the centre into a twisted knot or without form- 

 ing any protuberance. The crest-like plications, while diverging 

 across the expanded peripheral cup margins, gradually widen into 

 convex bands, separated by narrow linear furrows ; their surface is 

 ornamented with densely crowded granulations. The diameter of 

 the calyces is very unequal in the same specimens ; some of them 

 are three centimeters wide, others only one. The internal struc- 

 ture of the specimens I could never distinctly observe ; all the 

 specimens are transformed into a solid white amorphous mass of 

 carbonate of lime, resembling ivory or porcelain in a fracture, 

 while other corals associated with them had their most delicate 

 details of structure perfectly preserved, excepting one other here- 

 tofore described (Chonophyllum ponderosum), which is found in 

 similarly solidified condition. 



It is found in the light-colored limestones of the Hamilton 

 group, forming the lowest beds in the quarries of Phelps* lime- 

 kilns, near Alpena, and in a similar rock near Broadwell's mills, on 

 Thunder Bay River. 



Plate XXXVIII. — Fig. i is a calcified specimen from Broadwell's 

 mills, in natural size. 



In the Hamilton group of Rockford, Iowa, a coral is found 

 which bears an almost perfect similarity to the form just described, 

 exhibiting a well-preserved structure, consisting of membraniform 

 layers of confluent radiated cell cups, interlaminated with strata of 

 coarse, blister-like vesicles, entirely conformable with the structure 

 of a Strombodes from the Niagara group. The lamellae unite in 

 the depressed central pits in a low obtuse boss. Mr. Hall has 

 described this coral under the name of Smithia Johnnai, and 

 another similarly built form as Smithia multiradiata, but they 

 differ altogether in structure from the genus Smithia, or, what 

 I consider as the same thing, from Phillipsastrasa. The latter 

 genus has the structure of the usual forms of the compound 

 Cyathophylla, differing from them only by the absence of walls 

 separating the single cell cups, while the specimens under consider- 

 ation are built according to the plan of Strombodes ; and, guided 

 by perfect external similarity, I also identify the structureless 

 specimens found in Michigan, with Strombodes. 



