ISOTELUS, ACROLICHAS, CALYMENE, AND ENCRINURUS 79 
margin, originally must have been nearly 95 mm. in length. 
The glabella has about the same structure as the glabella of the 
other Silurian species here described; it is relatively long, the 
anterior part tends to be quadrangular, and the dorsal furrows 
do not diverge strongly posteriorly. The chief difference from 
Calymene vogdesi consists in the narrower anterior border which 
is not separated from the anterior part of the glabella by a groove 
distinct from the general curvature of the border. Compared 
with Calymene celehra Raymond (Bull. Mus. Comp. Zool. Har- 
vard Univ., 60, 1916, p. 28, pi. 3, figs. 9, 10) its anterior border 
is considerably wider. Of the pygidium not much is known, but 
the shallow groove along the top of the' ribs appears nearer the 
posterior margin of these ribs, at least along their distal half. 
All of the Trenton and Cincinnatian species of Calymene in 
American strata known to the present writer have the abbre- 
viated form of glabella, with the strongly divergent dorsal fur- 
rows. All of the Medinan and Niagaran species have the more 
elongate form of glabella, with the more moderately divergent 
dorsal furrows. The Trenton species include Calymene senaria 
Conrad, and Calymene abhreviata Foerste. The Cincinnatian 
species include Calymene granulosa Foerste, C. meeki Foerste, 
C. retrorsa and variety minuens Foerste, C. fayettensis Slocom, 
and C. gracilis Slocom. Calymene callicephala Green may have 
been founded on a poorly preserved erratic specimen of Calymene 
senaria. The Medinan species include Calymene vogdesi Foerste, 
and the Niagaran species include Calymene niagarensis Hall, 
C. hreviceps Raymond, C. celehra Raymond, and C. cedarvillensis 
Foerste. 
Encrinurus ornatus Hall and Whitfield 
Plate XVIII, figs. 9 A, B 
Encrinurus ornatus Hall and Whitfield, Pal. Ohio, 2, 1875, p. 154, pi. 6, fig. 16. 
The type of Encrinurus ornatus was found in the Cedarville 
dolomite at Cedarville, Ohio. It is doubtful whether this species 
occurs at any other horizon than in the Cedarville dolomite, 
although closely similar forms occur at other horizons. This 
species is found in the Cedarville dolomite not only at Cedar- 
