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 hlumenbachi var. niagarensis Hall, Pal. N. Y., 1852, pt. 2, p. 307, 



pi. 67, f. 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 hlumenbachi type, 

 that is with a narrow lip in front of the glabella, three pairs of glabellar 

 lobes, anrl pygidium with an impressed line on each rib, distinctly 

 bifurcating 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 IMaysville at Cincinnati, shows only a 

 trace of an impressed line on the ribs, and often the line is absent 

 entirel\'. 



Calymene breviceps, sp. nov. 



Plate 3, fig. 11. 



■Calymene niagarensis Hall, 28th Rept. N. Y. state mus. nat. hist., doc. ed., 

 1877, pi. 32, f. 8-15; mus. ed., 1879, pi. 32, f. 8-15; 11th Rept. Dept. 

 geol. and nat. hist. Indiana, 1882, p. 331, pi. 34, f. 8-15. Hall and 

 Clarke, Pal. N. Y., 1888, 7, pi. 1, f. 10-14. 



