TRILOBITES. 729 
Pterygometopus sehmidti.] 
lobes have the same relative size as in P. intermedius; but the separating furrows 
are very short, deeply incised at their inner extremities, while the lobes themselves 
are all confluent along the dorsal furrows. 
A single step further in the obliteration of the second lateral furrows, causing 
the first and second lobes to become wholly confluent, would produce that condition 
of the glabella which Schmidt has regarded of subgeneric value, proposing for 
species of this structure the name Monorakos* (Monorachus emend.). With the 
evidence of close specific relationship between P. eboraceus and P. intermedius, it 
would be inadmissable to employ this term here, though the former may be regarded 
as a stepping stone from the typical Pterygometopus to that condition of extreme 
coalescence of the glabellar lobes exemplified by Monorachus, 
Fig. 49.—Cephalon of Pterygometopus eboraceus, from the same specimen; somewhat restored. x 2. 
The occipital ring of P. eboraceus is broader than in P. intermedius and bears a 
conspicuous tubercle at its center. Genal spines are also present. The surface of 
the glabella is generally tubercled, and on the free cheeks there are faint, ramifying, 
minutely punctated grooves. The general form of the thorax is somewhat less 
tapering than in P. intermedius. 
The pygidium is scarcely triangular, the lateral slopes gentle. The axis bears 
about ten annulations, and the pleure eight ribs which are quite flat, separated by 
very narrow furrows, the first of which is shorter than the rest, becoming obsolete 
at a considerable distance from the margin; six of the ribs bear fine, oblique linear 
sulci. 
Formation and locality.—Trenton limestone, Rawlins Mills, N. Y. 
PTERYGOMETOPUS SCHMIDTI, 7. Sp. 
This name is proposed for a species whose features are altogether characteristic, 
though no single example has been observed which retains all the parts. Most of 
the specimens are heads and tails, and the best of them a cephalon with nine 
thoracic segments. As the characters of the more common species of the Minnesota 
rocks, P. intermedius, have been described, it will be sufficient to point out the 
differential characters of P. schmidti, which does not vary from the former in general 
s1ze. 
*Ueber einige neue ostsibirisehe Trilobiten und verwandte Thierformen; Bull. de Vacad. impér. des Sciences de St. 
Petersb,, p. 415, 1886 (Type, Phacops lopatini, Schmidt; pl. xii, figs. 6—9). 
