754 THE PALEONTOLOGY OF MINNESOTA. 



[Prootus parvlusoulus. 



HOPLOLICHAS, Dames. Frontal and lateral lobes equally convex; occipital lobes present. Occip- 

 ital ring with median simple or forked spine. No typically developed representative of this 

 group is known to occur in American faunas. The fossil described as L. (Hoplolichas) hylceus 

 Hall, from the Upper Helderberg group, known only from a portion of itscephalon, appears to 

 be the nearest of any to this type of structure. 



CONOLICHAS, Dames. Frontal lobe highly elevated or conical. Occipital lobes conspicuous. 



Pygidiutn with two pairs of falcate spines and a broadly bispined terminal lobe. 

 C. cornutus Clarke. Trenton. 



The L. (Conolichas) pustulosus Hall, of the Lower Helderberg, has a totally distinct 

 form of pygidium, with but two pairs of broad lateral spines and a broad, undivided 

 terminal lobe, like some of the fornis of Homolichas, while the glabella with its 

 elevated frontal lobe is unlike that of the latter subgenus and more similar to 

 Conolichas, save in the absence of the occipital lobes. The composition of this 

 species is peculiar and it will probably be found to stand as a distinct type of 

 structure. L. (Conolichas) hispidus Hall, and L. (Conolichas) eriopis Hall, appear to 

 be less like the normal Conolichas of the Silurian than the typical Arges of the 

 Devonian. 



There are some American species which can not be placed with any of the 

 foregoing divisions. Of these the one best known in all its parts is the L. halli 

 Foerste (with which L. faberi Miller is synomymous), from the Hudson River group 

 of Cincinnati, Ohio. This species is close in all structural features with L. margari- 

 tifer Nieszkowski, from the Lyckholm beds of the Baltic provinces, or uppermost 

 Lower Silurian; and for the latter Schmidt was unable to find a place among any of 

 the subgenera adopted by him. The head has a broad and not very convex frontal 

 lobe, sharply isolated lateral lobes, distinct occipital lobes and prominent ocular 

 nodes. The pygidium has two broad spines on each side, and a rounded terminal 

 lobe divided by a short and sharp median incision. 



PROETUS PARVIUSOULUS Hall, 1866. 



Proetus parviusculus HALL, 1866. Adv. Sheets, Twentieth Rept., N. Y. State Cab. Nat. Hist., p. 17. 

 Proetvs parviusculus HALL, 1872. Twenty-fourth Rept., N. Y. State Mus. Nat. Hist., p. 223, 



. pi. vm, tig. 14. 



Proetus parviutculut HALL and WHITFIELD, 1875. Palaeontology of Ohio, vol. ii, p. 109, pi. iv, 

 flg. 18. 



A few fragments, cranidia, free cheeks, and a single pygidium, of this species 

 have been observed in rocks from the base of the Galena shales at St. Paul. Some 

 of the glabellas, through compression, have the lobation more distinct than in the 

 usual forms from Cincinnati; and in all, the granulation of the entire surface is a 

 conspicuous feature. (Collection of Mr. Ulrich). 



