Silurian Fossils 
95 
; Rhynchotreta thebesensis occurs in a layer of rather coarse 
I grained crystalline limestone, 3 feet thick, forming the top of the 
5 exposure along the river bank a mile north of Thebes. This layer 
1 contains Lichas breviceps-thebesensis, a form differing from the 
I variety clintonensis only in having a pygidium of a slightly more 
j triangular outline than the common Clinton variety. In addition 
I to this, pygidia occur which cannot be distinguished from Phacops 
\ pulchellus, and others which {vomDalmamtes werthneri oniy 
in having a terminal spine, i mm. in length. Whitfield ell a billtng- 
siana, Meek and Worthen, is closely related to Whitfeldella cylin- 
drica. Pterinea thebesensis, Meek and Worthen, may be related 
to Pterinea rhomboidea, Hall. A try pa calvina, Nettleroth, not 
known from strata as early as the Clinton elsewhere. Leptcena 
i- rhomboidalis. Lyellia thebesensis, forming massive coralla with 
the walls of neighboring corallites almost in contact with each 
other, leaving very small interspaces for the coenenchyma. The 
tabula average about 8 or 9 in a length of 5 mm., and the plates in 
the intermediate spaces are more numerous, but not distinctly vesic- 
ular. The diameter of the corallites is slightly more than i mm. 
The walls of the corallites are slightly crenulated, and are slightly 
striated lengthwise. No septa are visible. See figures 69 A B 
on plate IV of this Bulletin. 
Beneath the coarse grained limestone carrying the preceding 
fauna there is a layer of clay shale one foot thick, underlaid by a 
layer of limestone, seven inches thick, containing Dalmanites dancE, 
Meek and Worthen, Schuchertella subplana, Pterinea thebesensis. 
Meek and Worthen, and a large form resembling Menstina maria. 
These species of Dalmanites, Orthothetes, and Menstina suggest 
later age than the Clinton of Ohio, so that the overlying fauna may 
be regarded as of later than Clinton age, but with a recurrence of 
some species elsewhere known in the Clinton. 
Beneath the Dalmanites danee layer, there are found, in descend- 
ing order, shale 2 inches thick; limestone, 4 inches thick, wavy at 
the base; shale, 14 inches thick; a layer of limestone, 8 inches 
thick. The latter contains Cyphaspis girardeauensis, Shumard; 
Proetus depressus, Shumard; Encrinurus deltoideus, Shumard; 
Acidaspis halli, Shumard: Orthis {? Schuchertella) missouriensis, 
Shumard; Leptcena (fBrachy prion) mesacosta, Shumard; T enta- 
culites incurvus, Shumard, and a species of Cornuhtes. This layer 
evidently contains the fauna described by Shumard from the Cape 
