42 Correlation of the Lower Silurian — Ulrich. 
gradually much less abundant. The lithological features, how- 
ever, are not remarkably different from those pertaining to the 
lower eighty feet. 
The beginning of the subdivision, as shown in the Cincinnati 
hills, about 360 feet above the river, is marked by the first ap- 
pearance of a number of easily recognized fossils, among them 
being Strofhomena fracta^ Orthis sinuata^ Platystrophia lati- 
costata^ Honiotrypa obliqua^ Batostomella gracilis^ Monticuli- 
J)ora molesta^ and Heterotrypa P vaupeli. Of these the first and 
the last two are restricted to the lower ten feet, but the others 
range upward eighty feet or more. It is at about this horizon 
also that Glyptocrimis dyeri, G. subglobosus,, Ohiocrinus con- 
^trictus,, Stenocrinus fetitagonus and locrinus subcrassus are 
found. 
Between 370 and 3S0 feet above low water mark there comes 
an a bed holding countless shells of a form of Stropho?nena 
which, on account of its exceptionally heavy shell, is known to 
collectors under the name ponderosa. Many of its valves (usu- 
ally the concave side) are encrusted by the delicate zoaria of 
Stomatopora and Atactoporella^ but lamellibranchs, gasteropods 
and other brachiopods are almost excluded from the bed by the 
prolific multiplication of the Strophomena. 
The next recognizable horizon occurs at an altitude of about 
385 feet above low water mark. This might be called the 
Strophoitiena iiasuta horizon, that restricted shell being very 
abundant here. From here on to the 400 feet level the shales, 
of a lighter color than usual, predominate. These shales pre- 
sent a wonderful development of life, the fossils being both 
beautifully preserved and of great variety. The class bryozoa, 
however, furnishes by far the greatest number of individuals as 
well as species. Fragments of Callopora ramosa^ C. rugosa^ 
Peronopora cotnpressa^ ]\Io7itictdipora ci?icinnatiensis^ Hetero- 
trypa inflecta^ Dekayia appressa^ Batostoniella gracilis^ Lepto- 
trypa ornata^ L. calceola, L. clavacoidea, and Cheiloporella 
flabellata are more or less abundant. With one or two excep- 
tions these species are also all restricted to this bed. Other 
•characteristic fossils of this horizon are Orthis jamesi\ Bucania P 
costata^ A?nbonychia P jafnesi and Ano?nahcrimis caponifortnis ^ 
The last well marked and, perhaps, the best known fossil 
