76 DISCOVERY OF TRENTON LIMESTONE. 
the organism described originally in the New State Re- 
ports as a fucoid, under the name ‘‘ Phytopsis cellulo- 
sum.’’ My own examination of these Pleasant Valley 
specimens makes it quite certain that it cannot bea fu- 
coid, but that it is a coral of the genus Tetradium ; its 
correct name is, therefore, Tetradium cellulosum. It is 
assigned in the Reports to the Birdseye Limestone, and 
has generally been considered characteristic of that pe- 
riod ; but here it is certainly a Trenton fossil. Mr. C. EH. 
Beecher informs me that he has found it also in the Hud- 
son River Group in Kentucky. But the feature of chief 
interest is the occurrence of Ostracoid Entomostraca in 
great abundance, and in quite a number of different spe- 
cies, described and undescribed. Beyrichia striato-mar- 
ginata, heretofore found only at Oxford, Ohio, is one of 
the most interesting of these. It is minute in size, being 
scarcely visible without a pocket magnifier. It is distin- 
guished by its D-shape and its broad, finely-striated bor- 
der. In Ohio, it is found in what is called the Cincinnati 
Group—the equivalent of the Trenton, Utica Slate, and 
Hudson River commingled. 
Two other exceedingly minute species are found here, 
which are probably Isochilina. lLeperditia fabulites, a 
well-known form found abundantly in Canada, and in 
the States along the Ohio River, occurs here. 
The remaining ostracoids will require much study for 
complete identification, but the following Canadian spe- 
cies appear to be present: Leperditia Anticostiana, Cana-_ 
densis, Josephiana, Louckiana and Ottawa ; also Isochi- 
lina gracilis. Some of these forms are credited in Can- 
ada to the Black River Limestone, some to the Chazy, 
some to the Utica Slate, Trenton and Hudson River 
Group. . Here they are all in Trenton. Of the ostra- 
coids which are probably new species, there is a fine tu- 
berculated Beyrichia, and there are quite a number of 
26 
