64 Cincinnati Society of Natural Fiistory. 
CRUSTACEA. 
Asaphus gigas DeKay. Lepidocoleus jamesi (Hall and 
4 maximus Locke. Whitfield). 
Calymmene callicephala Green. Primitia perminima Ulrich. 
Ceratopsis intermedia Ulrich. Primitiella unicornis Ulrich. 
Gerasaphes ulrichanus Clarke. Trinucleus concentricus Eaton. 
Ulrichia bivertex Ulrich. 
POSITION UNCERTAIN. 
Bythotrephis gracilis Hall. Lockeia siliquaria James. 
: gracilis-crassa Hall. Solenopora compacta (Billings). 
THE CINCINNATI PERIOD. 
The formation comprising the surface strata of south- 
western Ohio, southeastern Indiana and northern Kentucky, 
early known as the Blue Limestone, afterwards as the Cin- 
cinnati Group, has now come to be considered one of the 
major divisions of the Ordovician or Lower Silurian Era, 
with the title Cincinnati Period. As a whole it consists of 
clayey or marly, bluish or yellowish shales alternating with 
even-bedded, rather thin layers of limestone, the latter 
usually bluish and abundant enough to justify the early 
designation of Blue Limestone Formation. Occasionally 
there are layers containing considerable grit. ‘Towards the 
close of the period considerable beds of sandy material were 
deposited in some places; e. g., the Cumberland sandstone 
of Kentucky. 
While formerly considered a homogeneous whole, even 
with the Trenton strata of West Covington included, the 
Cincinnati period is now known to be easily separable into 
three divisions important enough to justify the application 
of the term group. ‘These divisions in descending order are: 
3. Richmond group, . . . between 200 and 300 feet thick. 
2: Lorraine: SrOuUp, 2: so.) co. se Oa ole ERO Mee ere Haelcs 
Te WiklearSrOu sn. ene Ae - 2) 2 8 200 feet thick: 
Total, TUS pints rs eee sre a7 0-6 7Oseem 
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