748 THE PALEONTOLOGY OF MINNESOTA. 
[Platymetopus bicornis. 
subgenus Platymetopus. I regret being unable to concur with Mr. Ulrich’s reference 
of this and the following species to Dames’ proposed subdivision Hoplolichas, but in 
the latter the third lobes are well defined. Dames ascribed much importance to, 
and indeed, found the suggestion of his term in the stout, sometimes forked spine 
borne by the occipital ring,* while the possession of anterior extensions of the frontal 
lobe, though of much the same significance structurally, is taxonomically unessential. 
It would seem, in fact, that if there is any basis for the admission of the division 
Hoplolichas, it lies in the presence of this ornamental or defensive character. The 
original specimen of P. robbinsi is broken near the center of the occipital ring but 
there is no indication that it possessed a central nuchal spine. 
In the possession by different subgenera of Lichas, of similar frontal extensions 
of the glabella, as in L. (Metopias) pachyrhyncha, var. longirostrata Schmidt, L. 
(Hoplolichas) proboscidea Dames and L. (Platymetopus) robbinsi Ulrich, we find an 
instance of morphic equivalence in a certain structural character coexisting with 
subgeneric features essentially distinct. 
Formation and locality.—Platymetopus robbinsi is from the middle beds of the Galena limestone, at 
Wykoff, Minnesota. (Collection of Mr. E. O. Ulrich). 
PriatyMETopus Bicornis Ulrich, (sp.), 1892. 
Lichas (Hoplolichas) bicornis ULR1cH, 1892. Two new Lower Silurian species of Lichas (Subgenus 
Hoplolichas); Amer. Geologist, vol. x, p. 272, figs. 2a-b. 
This interesting species has precisely the same character of glabellar lobation 
as the preceding, and the remarks made upon the generic relation of the former 
apply as well to this. In the possession of a pair of divergent spines on the frontal 
lobe it would seem to bear a similar relation to Hoplolichas tricuspidata Beyrich, as 
P. robbinsi does to H. proboscidea. The characters of the species, as far as known 
from a single cranidium, have been sufficiently described by Mr. Ulrich, and will be 
apparent from the accompanying figures. 
Figs. 70, 71.—Cranidium of Platymetopus bicornis Ulrich, with outline profile. 
Formation and loality.—Hudson River group; two miles east of Spring Valley, Minnesota. (Collection 
of Mr. E. O. Ulrich). 
*See Dames, Zeitschr. d, deutsch, geolog. Gesellsch., vol. xxix., p. 794, pl. 12-14, 1877. 
