76 
BULLETIN OF THE LABORATORIES 
PALEONTOLOGY. 
The Clinton Limestone of Ohio is very fossiliferous. The fossils, 
however, are often difficult to obtain on account of the hardness of 
the rock and its irregular fracture, when submitted to the blows of a 
geologist’s hammer. For the same reasons the identification of gas- 
teropods becomes extremely difficult, since their apertures are scarcely 
ever seen. In one form alone are they of common occurence, Cy~ 
donerna bilix ; this fossil is of rather frequent occurrence in the upper, 
shaly part of the group, from which it sometimes weathers with the 
neatness of Lower Silurian fossils in this State. Some forms of bra- 
chiopods preserve their outlines very indistinctly. This is true of 
Orthis flabella and the small form I have ventured to call O. elegantula, 
var. parva. Others are found only as single valves firmly held by 
the rock so that only one face, the external or internal, is presented. 
On this account it is difficult to associate dorsal with ventral valves, 
internal with external features. A few forms, however, occurring in 
the higher, more shaly strata, are frequently found well preserved, with 
both valves connected. Such are Orthis hyhrida^ O. eleganiula, and 
Rhyiidionella scobina. O. biforata f. Clintonensis and Triplesia Ortoni 
most frequently are found as fragments embracing that portion of the 
valves surrounding the beaks ; these fragments show both t^e external 
and internal features. They are also, although not as frequently, 
found as entire shells, with both valves united. Eidiwaldia retic- 
ulata, Orthis fausta, and Me7dstella umbonata, the last from the 
middle of the formation, have all been found as entire shells. The 
trilobites are usually found as fragments, the heads and tails being 
disconnected. In Illcenus the movable cheeks and glabellae are thus 
found separated. In only one specimen of Dahnanites Werthneii 
the intermediate articulations of the thorax were discovered. The 
association of glabellae and pygidia, therefore, is somewhat difficult. 
Still with all these failings, the fossilized forms of the Clinton Group 
deserve careful study, and to the careful and painstaking collector they 
will form one of the most productive fields of labor in the State. 
The fossils of the Clinton Group differ from the remains of the su- 
perposed Niagara formations of the State in this important particular, 
that, whereas the latter are most frequently found in the form of casts, 
the former almost always present the external features. Hence they are 
more readily determined and their structure can usually be easily studied 
by means of microscopic sections. In the following pages a full ac- 
