May, 1919] • Silurian Fossils From Ohio 395 



With this genotype, Synhomalonotus tristani Pompeckj (Loc. 

 cit., p. 247) erroneously associated an American species, 

 Calymene christyi Hall (13th Rep. New York State Cab. Nat. 

 Hist., 1860, p. 118; loth Rep., ibid., 1862 pi. 10, 'figs. 2-5), 

 from the Waynesville member of the Richmond, in Ohio, as 

 Synhomalonotus christyi. That this association is incorrect is 

 shown by the distinctly different structure of the glabella of 

 the latter. 



In Calymene christyi Hall (Ottawa Naturalist, 31, 1917, PI. 6, 

 Fig. 29) the glabella is only moderately convex from side to side; its 

 outline anteriorly tends to be quadratic, and the lateral furrows are 

 relatively shallow. The anterior lip is flat, and does not curve strongly 

 from side to side. The stiaicture of the pygidium of this species is not 

 well known. In the case oi Calymene platycephala Foerste, (PI. XIX, 

 Fig. 16 A, B), from the Trenton of Tennessee, both the glabella and the 

 pygidium are known, and the structure of the latter is very character- 

 istic. Its lateral margin is deflected abruptly downward, the deflected 

 part remaining smooth, and the pleural ribs extend only as far as the 

 line of deflection. Calymene dubia Savage, (Plate XIX, Figs. 15 A, B), 

 from the Girardeau limestone of Alexander County, Illinois, is con- 

 generic, and another congeneric species, also in the Savage collection, 

 occurs in the Maquoketa, near Yorkville, Illinois. For this group of 

 species, beginning with Calymene christyi, the generic term Platycoryphe 

 is proposed. 



Since the pygidium of Calymene platycephala is better known at 

 present than that of Calymene christyi, the fonner is chosen as the 

 genotype of Platycorphye. The cranidia of all the forms here discussed 

 are known. 



Platycoryphe dubius, Savage. 

 Plate XIX, Figs. 15 A, B. 

 1913. Bull. Geol. Surv. Illinois, No. 23, p, 60, pi. 2, figs. 8, 9. 



The only characteristic feature noted in the cranidium was the 

 presence of a pit in each of the dorsal furrows, a short distance 

 anterior to the rather faint anterior pair of glabellar furrows. 



The sides of the axial lobe of the pygidium diverge at an angle of 30 

 degrees. The axial lobe is weakly defined, except along its posterior 

 third, which rises distinctly above the posterior parts of the pygidium. 

 The antero-lateral angles of the pleural lobes are obliquely and abruptly 

 deflected downward at an angle of about 130 degrees with the adjacent 

 part of the pygidium. This deflection is noted also in Platycoryphe 

 platycephalus Foerste, from the Trenton of Clifton, Tennessee, with 

 which the Girardeau species was compared by Savage. 



In Platycoryphe platycephalus, (Plate XIX, Fig. 16 A, B), the lateral 

 margin of the pygidium is abruptly deflected downward, the anterior 

 part of the deflected margin forming an angle of about 130 degrees 



