TRILOBITES. 747 
Platymetopus robbinsi.] 
peculiar subconical protuberance. It is mainly in the latter feature that the species, 
so far as its parts are known, differs from the Lichas trentonensis Conrad, A well 
preserved glabella of P. cucullus occurs among the material from the Galena lime- 
stone of Wykoff, Minnesota, loaned by Dr. Robbins, and a fragment which may 
represent the same species comes from the Trenton beds at Janesville, Wisconsin 
(Museum No. 5414). 
PratymMeropus roppinst Ulrich, (sp.), 1892. 
Lichas (Hoplolichas) robbinsi ULRicH, 1892. Two new Lower Silurian species of Lichas (Subgenus 
Hoplolichas). Amer. Geologist, vol. x, No. 5, p. 271, figs. la-b. 
The original and, as far as [ am aware, the only observed specimen of this 
species, is a cranidium lacking only the anterior portion of the glabella. The species 
is an interesting addition to the American lichads and presents some especially 
noteworthy features. Among these is the stout baculiform anterior extension of the 
frontal lobe of the glabella, which appears to be homologous with the produced 
lobe of the well known lower Silurian species, L. celorrhin Angelin* and L. pachy- 
ryncha Dalman, var. longirostrata Schmidt,; rather than with such spinous processes 
as those possessed by L. bicornis Ulrich, Hoplolichas tricuspidata Beyrich and H. 
proboscidea Dames. 
~ The character of the glabellar furrows, also, is of importance. These are very 
narrow and sharply impressed, have the usual degree of curvature anteriorly, but 
posteriorly become quite parallel and straight, debouching in the equally narrow 
occipital farrow at right angles. Thus, as in so many of the American Silurian 
species of Lichas, these grooves represent the continuous anterior and posterior 
furrows, the median pair being lost by the coalescence of the first and second lobes. 
The third pair of lobes we regard as obsolete. 
Figs. 68, 69.—The cranidium of Platymetopus robbinsi Ulrich; with outline profile. 
Elsewhere we have expressed the conviction that the lobation of the glabella 
must be given first importance in the subdivision of the genus Lichas, and the nature 
of this lobation with the total loss of the third lobes places this species with the 
* Palwontologia scandinaviea, pt. i, p. 69, pl. xxxv; figs. la-c, 1878. 
+Schmidt, Revis. d. ostbalt. Silur. Trilob. ii. Acidaspiden u. Lichiden, pl. i. fig. 12. 1858. 
