IT2 LOWER PENINSULA. 



matcly united, polygonal stems of similarly variable sizes, and 

 unequal in the same specimens through the intermixture of fre- 

 quent young cells. Calyces moderately deep, obliquely spreading 

 in the margins, and more abruptly excavated in the inner circumfer- 

 ence. Bottom of cups reflected into a large, conical protuberance, 

 carinated on the sides by the converging ends of the radial lamell.-E, 

 and terminating with a laterally compressed cristiform edge. 

 From thirty to forty lamellae in the circumference of a calyx ; and 

 sometimes indications of rudimentary, intermediate plications are 

 noticeable. The clusters of singly growing stems cover sometimes 

 spaces of large extent, and not a specimen with astraeiform, poly- 

 gonal calyces is found among them ; in other localities the astraei- 

 form colonies are the prevailing form ; this seems to indicate a 

 difference between the two forms, but specimens are found, and 

 that not rarely, in which one part of the stems is free, circular, and 

 another intimately united, pressing each other into the polygonal 

 form. As no difference in the structure can be observed in the 

 two forms, I am inclined to consider them modifications of one 

 species, whose difference in mode of growth is perhaps only de- 

 pendent upon local conditions existing at one and another place. 

 Occurs in the carboniferous limestone of Wildfowl Bay, and at 

 Bellevue and Grand Rapids, Michigan. 



Plate LV. — The upper tier represents two specimens from the 

 carboniferous limestone of Wildfowl Bay — one with astraeiform, 

 polygonal calyces, the other with partial free circular stems. 



The specimen lying across the bottom of the lower tier in the 

 .same plate is a singly grown stem of the same species. 



BLOTHROPHYLLUM, Billings. 



Conico-cylindrical polyparia, single, or in cespitose clusters, pro- 

 duced by prolific calycinal gemmation of a few parent cells. The 

 structure of the stems, as being built of a . series of invaginated 

 cups, is particularly obvious. The bottom of these cups has the 

 shape of transverse diaphragms, smooth in the centre, or super- 

 ficially carinated by the central ends of the radial, crest-like folds, 

 into which the side walls of the cups are plicated. These crests of 

 the superimposed cups unite into continuous vertical laminae within 



