I06 LOWER PENINSULA. 



CYATHOPHYLLUM DAVIDSONI. 



Synon., AcERVULARiA DAVIDSONI, Milne-Edwards. 

 ACERVULARIA PROFUNDA, Hall. 



The corals described under the name Acervularia Davidson! and 

 Acerv. profunda, which latter I consider merely as a variety of the 

 former, are in structure identical with Cyathoph. rugosum. The 

 genus Acervularia is represented as having its central portion of the 

 polyp cells surrounded by an internal wall, but neither the above- 

 mentioned corals nor the typical forms of the genus Acervularia 

 (Cyath. pentagonum and Cyath. ananas of Goldfuss) exhibit an in- 

 ternal wall. In the circumference of the abrupt inner cell-pits of 

 all these forms a sort of annular demarkation is conspicuous in 

 transverse sections, because the shorter ones of the alternately 

 larger and smaller radial lamellae terminate there with somewhat 

 thickened edges, but they never combine into a closed, ring-like 

 wall. 



The specimens described by Milne-Edwards are from the Helder- 

 berg limestones of the Falls of the Ohio ; the Michigan forms 

 identified with it in the subsequent description are found in the 

 Hamilton group. 



Growth in large, convex masses, or in lenticular, discoid expan- 

 sions, covered in the lower depressed, conical, and centrally at- 

 tached side with a concentrically wrinkled epithecal crust. Stems 

 multiplying by marginal and central gemmation from the calyces ; 

 sometimes single stems are free and circular ; usually the growth 

 is astra^iform, with intimately connected polygonal calyces, sur- 

 rounded by acute linear crested edges. The margins of the calyces 

 are usually broadly explanate, discoid, rarely gradually descending 

 into the more abrupt, bell-shaped, central excavation proper to 

 all forms, on the rounded bottom of which the lamelhi; unite, or 

 which, in rarer instances, exhibits a narrow diaphragm sparsely 

 intersected by lamellar crests. Diameter of calyces about one 

 centimeter, but quite variable. Lamellae long and short, in alter- 

 nation, but equal in size near the calyx margins, crenulated at the 



