254 The Ohio Journal of Science [Vol. XVII, No. 7, 



Trochurus nasutus, Weller, from the Racine division of the Niagaran 

 near ^Milwaukee, Wisconsin, differs chiefly in the anterior prolong^ation 

 of the median lobe into a spine. The lateral extremities of the third 

 lateral lobes are not elevated nor conspicuously spinose. The occipital 

 lobes are not conspicuous. 



Trochurus welleri, Nov. sp. (Corvdocephahis phlvdainodes. Weller, 

 1907, Bull. Chicago Acad. Sci., Nat. Hist. Surv., 4, pt. 2, p. 234, pi. 22, 

 figs. 1-4), from the Racine division of the Niagaran near Lemont, Illi- 

 nois, resembles Trochurus hanoverensis in the more even curvature of its 

 median lobe from front to rear; however, the anterior marginal part is not 

 curved as far backward, and the curvature is only moderate near the 

 posterior end of this lobe. In addition to the conspicuous spines ter- 

 minating the lateral ends of the third lateral lobes, there is a conspicuous 

 pair of spines on the median lobe, anteriorly. Named in honor of Prof. 

 Stuart Weller, of Chicago University. 



Trochurus halli, Nov. sp. Plate XII, Figs. 4A-D; {Arges phlvctain- 

 odes, Hall, 1852, Pal. New York, 2, p. 314, pi. 70, figs. 2a-2c), from the 

 Rochester shale near Albion, New York, is closely related to Trochurus 

 bvrnesanus. It differs chiefly in the curvature of the median lobe of the 

 glabella, from front to rear; this ciu-vature is greater anteriorly, but it is 

 not strongly accentuated antero-dorsally, nor accompanied by a straight- 

 ening of the dorsal outline as in that species. Viewed from the dorsal 

 side, the anterior part of the median lobe is less prominent, the furrows 

 separating the third lateral lobes from the compound anterior lateral ones 

 diverge more to the front laterally, and there is no indication of spines 

 terminating the lateral ends of the third lateral lobes. Named in honor 

 of James Hall, the great founder of American Paleozoic Paleontology. 



A line of progression should extend apparently from Tro- 

 churus halli, in the Rochester shale, through Trochurus byrne- 

 sanus, in the Laurel limestone, to Trochurus nasutus, in the 

 Racine division of the Niagaran. 



Trochurus hanoverensis, from the Laurel limestone and 

 Trochurus welleri, from the Racine evidently belong to another 

 group. From one of the earlier members of this group, Tro- 

 churus phylctainodes could have diverged by a more bulbous 

 development of the posterior end of the median lobe and a 

 greater downward extension of the anterior parts of the cephalon. 



Prof. Percy E. Raymond has called to my attention that 

 Corydocephalus is antedated by Trochurus as follows: Trochurus 

 was founded by Beyrich in 1845 (Ueber Bohm. Tril. p. 31, pi. 1, 

 fig. 14) on Trochurus speciosus, sp. nov. (Beyrich), this species 

 being illustrated by a figure of the pygidium, the name Tro- 

 churus (wheel) alluding to the general appearance of the pygi- 

 dium (a wheel with spokes). Unfortunately Beyrich described 

 under Trochurus speciosus also the head of a Staurocephalus. 



