68 LOWER PENINSULA. 



THECIA RAMOSA, N. Sr. 



Stout, branching, and sometimes reticulated, anastomosing stems, 

 from half an inch to two inches in diameter, composed of thick- 

 walled, conico-cylindrical tubes ascending and diverging from a 

 central imaginary axis. Orifices unequal, of polygonal form, from 

 one to two millimeters wide at the edges of the dilating margins, 

 radiated by twelve prominent spinulose crests, extending through 

 the Avhole length of the channels. Transverse diaphragms partly 

 simple and complete, partly incomplete, represented by lateral 

 squamiform, horizontal leaflets. Pores large and very numerous. 

 Older stems are often much altered in appearance by excessive 

 thickening of their tube walls, and contraction of the tube channels, 

 with obliteration of the radial crests. It is sometimes difficult to 

 distinguish them from similarly altered stems of Favosites radici- 

 formis, with which they are found associated. Occurs in the upper 

 Helderberg strata of Mackinac Island, and is not uncommon in 

 drift boulders on the Southern Peninsula of Michigan. It is found 

 in great perfection and frequency in the Helderberg limestones of 

 the Falls of the Ohio. The silicified specimens represented on 

 Plate XXV., Pig. 4, are from the latter mentioned locality. 



VERMIPORA, Hall. 

 (Twenty-sixth Annual Report of the State Cabinet.) 



Ramified twigs, composed of contiguous, subparallel cylindrical 

 tubules, multiplying by lateral gemmation, slowly diverging in their 

 parallel ascending course from a central imaginary axis, and be- 

 coming disjunct near their peripheral ends, which project on the 

 surface as single proboscidal siphuncules. Tubes intersected by 

 remote transverse diaphragms, and connected by lateral pores. 

 Vertical radiating crests not observed. 



Mr. Hall places these forms with the Bryozoa, and gives of their 

 structure a description different from mine. He has overlooked 



