CLINTON GROUP. 
n 
I have obtained beautiful casts of this fossil in a light grey limestone (lower part of the 
“ cliff,”) from Springfield and Dayton, Ohio, and have seen them from several localities in 
Indiana. In Iowa I collected some fine silicified casts of the same, from the cliff limestone, 
on the Maquoqueta creek. It is therefore a widely distributed fossil, and when more 
thoroughly examined will doubtless be found typical of certain strata at the Avest, as in New- 
York. 
Fig. 6, the Delthyris brachynota accompanies the Pentamerus, and even continues long 
after that fossil has disappeared ; several specimens having been seen near Reynolds’ basin, 
in Niagara county. It is the only Delthyris known in this rock, and is readily recognized by 
the relatively short hinge line. 
The other fossils of the limestone are represented in the following woodcut; 
16. 
1. Orthis circulus. 
2. Atrypa congests. 
4. Atrypa plicatula. 
5. Crinoidal joint. (Natural size and magnified.) 
1. Orthis circulus. —This is a beautiful, circular, finely radiated shell, with a narrow area. 
It is found accompanying the Atnypa congesta at Reynolds’ basin. It is distinguished from 
a similar shell in the Hamilton group by its greater length on the hinge line, and the greater 
proportional width of the shell. 
2. Atrypa congesta (of Conrad). — West of the Genesee river, after the disappearance of 
the Pentamerus, we find the lower limestone of the group distinctly marked by the presence 
of this small Atrypa, which is exceedingly abundant at Medina, and near Reynolds’ basin^ 
It is associated with the crinoidal joints like fig. 5 of woodcut. It appears standing out in 
relief upon the surface of weathered specimens, which are abundantly strewed over the ground 
a mile or two south of Medina. Near Reynolds’ basin it occurs in great numbers, completely 
covering the surface of certain layers, and large numbers of separate individuals can be 
obtained among the decomposed portions. This shell appears to take the place of the Pen¬ 
tamerus so far as regards numbers of individuals, prominence, and place in the strata. 
It is a smooth shell closely resembling Atrypa linguifera of Murchison’s Silurian System, 
pi. 13, fig. 8 ; but the length of the latter appears to be greater in proportion, and the shell 
