34 bulletin: museum of comparative zoology. 



In spite of the similarity of Cheirurus niagarensis, as above defined, to 

 Cheirurus insignis, I believe that a separate specific name should be 

 maintained, especially as the discovery of further material may show 

 unsuspected differences between the two. 



Measurements: — A cranidium from Rochester (M. C. Z. 625). 

 Length 20 mm., width 35 mm. ; width of glabella at neck-ring 12 mm., 

 at front 16 mm.; length of frontal lobe 10 mm. A cranidium from 

 Wauwatosa, (M. C. Z. 626). Length 9 mm., width 18 mm.; width 

 glabella at neck-ring 5 mm., width at front 8 mm. ; length of frontal 

 lobe, 3 mm. 



Formation and locality: — Rochester shale at Rochester and Lock- 

 port, N. Y., Niagaran in Indiana, Wisconsin and Illinois. 



Cheirurus welleri, sp. nov. 

 Plate 3, fig. 6; Plate 4, fig. 7, 8, 10. 



Ceraurus insignis Hall, Pal. N. Y., 1852, pt. 2, p. 300, pi. 66A, f. 4. Geol. 



surv. Wise, 1862, 1, p. 433; 18th Rept. N. Y. state cab. nat. hist., 1865, 



p. 31, adv. sheets; 20th Rept. N. Y. state cab. nat. hist., 1868, p. 335. 

 ? Ceraurus bimucronatus Roemer, Silurian faun. west. Tenn, 1860, p. 80, pi. 5, 



f. 19. 

 Ceraurus niagarensis HaU, 20th Rept. N. Y. state cab. nat. hist., 1868, p. 376, 



pi. 21, f. 10-11; 1870, rev. ed., p. 427, pi. 21, f. 10, 11 ; 11th Rept. Dept. 



Geol. and nat. hist. Indiana, pi. 33, f. 10, non pi. 34, f. 16. WeUer, Bull. 



Chicago sci., 1907, no. 4, pt. 2, pi. 24, f. 21 (non 20). 



The most abundant American Silurian cheirurid in the collections 

 of the M. C. Z. is one whose glabellar furrows nearly cross the glabella, 

 and is therefore the nearest approach to a Crotalocephalus so far found 

 in America. This type has long been known, but constantly confused 

 with Ch. niagarensis or Ch. insignis. As has already been mentioned, 

 Hall figured one in 1852, and Roemer a similar one in 1860. The two 

 species sometimes occur together, as at Wauwatosa, but Ch. welleri is 

 easily recognized by its long glabellar furrows. A second distinction 

 is that the posterior margin of the hypostoma is rounded in Ch. 

 welleri and straight in Ch. niagarensis. Further, the hypostoma of the 

 latter species is tuberculated and of the former smooth. 



A large Cheirurus with approximately semicircular cephalon. The 

 glabella is long, expands gradually forward. The frontal lobe occu- 



