TRILOBITES. 737 
Note on Ceraurus.] 
glabella is continuous with the broad frontal margin of the cephalon. Of American 
species representing this subgenus we may cite: C. apollo and C. mercurius Billings, 
from the Quebec group, C. varus Walcott, from the Trenton limestone and C. scofieldi 
Clarke, from the Galena shales. 
In Pseudospherexochus the glabella is very convex, the third lateral furrow 
stronger than the others, and the third lobe larger and not separated from the body 
of the glabella. The pygidium bears eight marginal spines of subequal length. 
Under this division may be placed C. prolificus Billings, of the Quebec group, and P. 
trentonensis Clarke, of the Trenton limestone. 
Mieszkowskia Schmidt, has the glabellar furrows very oblique posteriorly, 
the glabella most convex behind and usually produced into a posterior spine; 
the third furrow is the strongest and the third lobe is not separated from the body. 
To this division may be referred Billings’ C. glaucus, and C. perforator, of the 
Quebec group, C. satyrus, of the Chazy limestone, and C. numitor of the Hudson 
River group. 
Schmidt includes among these subgenera, Spherocoryphe Angelin, in which the 
anterior portion of the glabella, embracing the frontal lobes and the first and second 
lateral lobes, becomes extremely convex and subspherical, without traces of lateral 
furrows. ‘The third lobes only are apparent, and these quite obscure. 
Of the foregoing divisions, all except Pseudospherexochus have a pauci-annulate 
pygidium, with usually two or three annulations and ribs, and the first pair of ribs 
much the largest and extended at their free extremities far beyond the rest. In 
Pseudospherexochus the eight free points of the pygidial ribs are sharp and angular. 
In Eccoptochile Corda, there are but six of these extensions and they are flat, broad 
and blunt at their extremities, and do not extend beyond the general marginal arc; 
while in Crotalocephalus Salter, these are likewise six in number, but narrow, 
incurved, distant, and acute. The structure of the glabella in Hccoptochile clavigera 
Corda, the type of the subgenus, is essentially similar to that of Cerawrus, though 
the glabella is rather more rotund and ovoid; but in Crotalocephalus there is a large, 
convex and protuberant frontal lobe. The first and second lobes are short and 
horizontal, and the third or basal lobes isolated by the union of the third glabellar 
furrows with the occipital groove. Lccoptochile is represented in the Hudson River 
fauna by Ceraurus icarus (Billings) Meek. Of the typical Crotalocephalus we 
probably have but one representative, the C. niagaraensis Hall, of the Niagara shales 
of Lockport and Rochester, N. Y., and the magnesian limestones of Illinois and 
Wisconsin. 
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