G. M. Ehlers — New Species of Tetracoralla. 461 



Aet. XXXIII. — Heterolasma foerstei, a New Genus and 

 Species of Tetracoralla from the Niagaran of Michi- 

 gan; 1 by G. M. Ehlees. 



The type specimen of this interesting coral, Hetero- 

 lasma foerstei, was collected from a cherty, brown, mag- 

 nesian limestone of thin, uneven-bedding. This rock 

 outcrops at the top of a very low, eastward-facing es- 

 carpment &bout half a mile south of Gould City, Macki- 

 nac County, Michigan. This limestone, now placed by 

 the Michigan Geological and Biological Survey in the 

 Manistique formation of the Niagaran of Michigan, in 

 the writer's opinion should be correlated with the Upper 

 Coral Beds of, Wisconsin and the Lockport of Ontario 

 and New York. 



The shape of the corallum, which is silicified and pre- 

 served in a fragmentary condition, was that of a short 

 cone, with the upper part widely expanded horizontally 

 (see fig. 1). The side of the corallum adjacent to the 

 cardinal septum has a slightly greater curvature. 



The epithecal covering of the outer surface is annu- 

 lated by low ridges and shallow grooves (see fig. 2). 

 Fine, close-set, concentric lines, probably representing 

 lines of growth, are obscurely shown on a few of the bet- 

 ter preserved portions of the epithecal surface. 



Stout radicif orm processes occur at irregular intervals 

 (see figs. 1 and 2). Some of the better preserved ones 

 exhibit a double tubular construction, produced by the 

 downward extension of the theca within the epitheca. 

 The two tubes seem to have been normally separated 

 throughout most of their length. This separation of the 

 thecal and epithecal tubes is clearly shown at the broken 

 end of the process indicated as r 1 on fig. 2. The same 

 structure is indicated in two other processes, r 2 and r 3 

 fig. 2, although the inner and outer tubes are much 

 obscured by deposits of chalcedony in the spaces between 

 them. 



The extension of the theca into the radiciform pro- 

 cesses has resulted in the formation of more or less cir- 

 cular openings in the wall of the calyx, which interrupt 

 the continuity of some of the septa. Several septa are 



1 Published with the permission of the Director of the Michigan Geolog- 

 ical and Biological Survey. 



