90 LOWER PENINSULA. 



COLUMNARIA ALVEOLATA, Goldfuss. 



Convex, large colonies, sometimes attaining a diameter of several 

 feet, composed of intimately connected tubes diverging from a 

 basal centre. Lower side covered by a concentrically wrinkled 

 epitheca ; central part attached. Tubes quite unequal in the same 

 specimens and in different specimens. In some they vary from 

 two to five millimeters ; in others, tubes one centimeter in width, and 

 smaller ones of only two and three millimeters, are intermingled. 

 Radial lamellae from twenty to forty, according to the size of the 

 tubes, not reaching to the centre. Transverse diaphragms flat, close- 

 ly set, usually smooth in the centre, and only at the outer circumfer- 

 ence intersected by the radial crests. It is rarely the case that the 

 lamellae extend as low carinations over the surface of the diaphragms 

 to the centre. The figures of Goldfuss exhibit the radii as alter- 

 nately reaching the centre ; this is, as already stated, very unusual 

 with specimens from the Trenton group, while it is regularly seen 

 in the specimens from the Hudson River group and Niagara group. 

 Milne-Edwards considers both forms as one species, but I think 

 they differ sufifiiciently to be set down as two species. To the 

 Trenton form Goldfuss's name, Alveolata, is applied by most of the 

 palaeontologists ; for the Hudson River group species, Hall's name, 

 Columnaria (Favistella) stellata, is adopted, although it is not per- 

 fectly certain whether Goldfuss had not also a Hudson River 

 group specimen under consideration. 



The Trenton strata of the Escanaba River and of St. Joseph 

 Island, in Lake Huron, contain an abundance of this coral, but the 

 specimens are not very well preserved, being transformed into 

 dolomite spar, which is a very unfavorable material for the pres- 

 ervation of the finer structural details. This cora) is also fre- 

 quently found in the Trenton group of Illinois, at Dixon, and in 

 the lead-bearing strata of Wisconsin and Iowa, where it is often 

 found in silicified condition, and finely preserved. 



Plate XXXIV. — Fig. i is the surface view of a specimen from 

 the Trenton group of St. Joseph Island. Fig. 2 is a fractured 

 surface exhibiting a vertical section of a specimen from Escanaba 

 River. Fig. 4 is a specimen with very large and unequal tubes, 

 found in the Trenton group, at Dixon, Illinois. 



