TRILOBITES. 727 
Pterygometopus intermedius, ] 
York forms. To indicate to the student and collector the structure of the entire 
animal I introduce a figure drawn from one of the New York specimens. 
Fig. 44.—Outline of Dalmanites achates Billings. Trenton Falls, N. Y. 
Subgenus PTERYGOMETOPUS, Schmidt, 1881. 
PreRYGOMETOPUS INTERMEDIUS Walcott, (sp.) 1877. 
Dalmanites intermedius Waxcorr, 1877. Adv. Sheets Thirty-first Rept. N. Y. State Mus. Nat. 
Dalmanites fee eee 1879. Thirty-first Rept. N. Y. State Mus. Nat. Hist., p. 69. 
Mr. Walcott’s species has not heretofore been figured, but after careful compar- 
ison with the description, and with the aid of the original specimen, I have little 
hesitation in referring to it the commonest of the species of Pterygometopus occurring 
in the Silurian rocks of Minnesota. Without entering into a detailed description of 
this form, which has been given by Walcott, some of its differential features may 
be emphasized. 
The outline of the cephalon is rendered subtriangular by a slight anterior 
projection of the margin. The facial sutures also make a slightly salient angle at 
this point, and frequently here the surface of the glabella is impressed or casually 
forced down. The anterior limbs of the suture cut off or traverse the lateral angles 
of the frontal lobe, as in all species of Pterygometopus; the posterior extension of 
these sutures over the cheeks is marked by an elevated line. The eyes are relatively 
small, their anterior angles not reaching the first glabellar furrows, while their 
posterior angles are distant from the occipital furrow. The glabella is characterized 
by the slight anterior or outward convexity of the first lateral furrows, the graceful 
rotundity of all the lobes and the decidedly depressed, though slightly convex 
median region between the first and second pairs of lateral lobes. On account of 
this depression the lobes are quite isolated and not confluent with the middle of the 
glabella. The second furrows are linear, deep only at their proximal extremities, 
but distinctly continued to the dorsal furrows. The third or occipital lobes are small 
