RAYMOND: NEW AND OLD SILURIAN TRILOBITES. 27 
CALYMENIDAE Milne Edwards. 
CALYMENE NIAGARENSIS Hall. 
Calymene niagarensis Hall, Geol. N. Y., 1843, pt. 4, p. 102, f. 3 on p. 101; tab. 
org. rem. 10, f. 3. 
Calymene blumenbachi var. niagarensis Hall, Pal. N. Y., 1852, pt. 2, p. 307, 
pl 67, 4. 11, 12, 
Calymenes are difficult fossils to differentiate satisfactorily, but it 
is possible to draw a little closer limits to some of the species than has 
been done in the past. The Silurian species do not present so difficult 
a problem as do those in the Ordovician, specific characteristics being 
apparently more fixed and constant in later times. Before venturing 
to separate two new species, it is best to direct attention for a moment 
to the well-known (in name) Silurian form. 
The name was applied originally by Hall to specimens from the 
Rochester shale at Lockport, N. Y. The figures and description show 
the original specimens to have been of the Calymene blumenbachi type, 
that is with a narrow lip in front of the glabella, three pairs of glabellar 
lobes, and pygidium with an impressed line on each rib, distinctly 
bifureating the outer portion. The ribs also reach practically to the 
margin. 
It seems that the species Calymene niagarensis should be restricted 
to such trilobites as show these important characteristics of the types 
and these may be seen in most of the Calymenes in the Rochester 
shale. Another Calymene found at the same horizon, C. vogdesi 
Foerste, has the same bifurcated ribs on the pygidium, but a much 
longer snout-like lip in front of the glabella. It is also a much larger 
form, one of the largest of the Calymenes. 
In the Ordovician the common Calymene senaria of the Trenton 
has the same type of bifurcated rib, while the later C. meeki Foerste, 
so abundant in the Eden and Maysville at Cincinnati, shows only a 
trace of an impressed line on the ribs, and often the line is absent 
entirely. 
CALYMENE BREVICEPS, sp. nov. 
Plate 3, fig. 11. 
Calymene niagarensis Hall, 28th Rept. N. Y. state mus. nat. hist., doc. ed., 
1877, pl. 32, f. 8-15; mus. ed., 1879, pl. 32, f. 8-15; 11th Rept. Dept. 
geol. and nat. hist. Indiana, 1882, p. 331, pl. 34, f. 8-15. Hall and 
Clarke, Pal. N. Y., 1888, 7, pl. 1, f. 10-14. 
