282 Cincinnati Society of Natural History. 
The Black River limestone in New York is usually a gray, compact 
or subcrystalline limestone, or blue compact limestone, and distin- 
guished by the remarkably large specimens of Orthoceras that occur in 
it. Some of them are ten feet in length, and a foot in diameter. The 
thickness is about 50 feet. In Vermont it constitutes the black marble 
of Isle La Motte, where its thickness is from 12 to 20 feet. . 
The Group spreads over quite an extensive area in Canada, rarely 
attaining any great thickness, though on the St. Lawrence 90 miles be- 
low Quebec, it has a thickness of 136 feet. Its existence has been 
noted in the Lake Superior region on St. Mary’s, Escanaba, and Me- 
nomonee rivers, on St. Joseph and Sugar islands, and at Plattsville, 
Wisconsin. In Missouri, it forms exposures 75 feet in thickness. In 
Pennsylvania, it is said to have very great thickness, but the geological 
surveys of that State have been so poor, and so much worthless syn- 
onymy has been injected into the reports that one can not acquire much 
information about its geology without personal examination, or with- 
out waiting until after a geological survey shall be organized anew. 
The distribution of the genera which commence an existence in this 
eroup is as follows: 
In the vegetable kingdom, Licrophycus occurs in the Trenton and 
Hudson River, and Phytopsis is peculiar to it. Among the Protista, 
Astylospongia occurs in the Trenton and Niagara, and Stromatocerium 
in the Trenton. 
Among the Polypi, Stromatopora and Petrata occur in succeeding » 
eroups as high as the Devonian; Calapecia occurs in the Hudson 
River and Clinton, and Yetradium in the Trenton and Hudson River. 
Among the Brachiopoda, Streptorhynchus occurs in nearly every 
succeeding group to the Permian; Dinobolus occurs in the Guelph; 
and Hichwaldia in the Niagara. 
Among the Pteropoda, Pterotheca occurs in the Trenton and Hud- 
son River. 
Among the Gasteropoda Loxonema occurs as high as the Permian; 
Hunema as high as the Devonian, and Orthostoma is peculiar to it. 
Among the Cephalopoda Gyroceras and Phragmoceras occur in 
various groups to the Subcarboniferous; Gomphoceras occurs as high 
as the Hamilton; Colpoceras and Gonioceras occur in the Trenton; 
and Conoceras is peculiar to it. 
Among the Lamellibranchiata, Conocardium occurs in various 
groups as high as the Subcarboniferous, and Lyrodesma occurs in the 
Trenton and Hudson River. a 
