76 LOWER PENINSULA. 



MICHELINIA TROCHISCUS, N. Sp. 

 Synon., AsTR.iiA stylophora, Eaton. 



Small hemispherical masses, not often exceeding the diameter of 

 two inches, usually smaller. The depressed conical or flat basal side 

 is covered by a concentrically wrinkled epitheca, and is attached by 

 a broad central scar to other marine bodies, to Gasteropod shells, 

 Crinoid stems, and very frequently to the surface of Fistulipora. 

 (See Worth. Geol. of Illin,, Vol. III., PI. 9, Fig. ib.) Tubes very un- 

 equal, rounded-polygonal, from four to seven millimeters wide. 

 Cavity longitudinally striate by numerous spinulose crests. Dia- 

 phragms irregular and not much crowded. Pores dispersed without 

 order. 



Occurs in the Hamilton group of Thunder Bay, and is very 

 common in the Hamilton group of New York. The small specimens 

 found in the upper Helderberg limestones of Michigan, Ohio, and 

 Indiana, which are the forms to which Pleurodittyum problema- 

 ticum has principally to be referred, are almost the same, if not an 

 identical form with Michelinia trochiscus. I have not figured this 

 species. 



MICHELINIA CLAPPII. 



Synon., ChonOSTEGITES Clappii, Milne-Edwards. 



Haimeophyllum Ordinatum, Billings. 



Michelinia intermittens, pars, Billings. 



Convex or discoid masses, formed of tubular, closely aggregated, 

 subparallel or diverging polyp stems, from five to eight millimeters 

 diameter, multiplying by marginal buds. Tubes annulated by 

 alternate constrictions and dilatations into an urn shape of the in- 

 termediate segments, having horizontally spreading margins, which 

 unite with those of the adjoining tubes, forming continuous laminar 

 floors, whereby the otherwise free tubes are held together and com- 

 municate with each other by transverse channels crossing the laminae. 



