Maryland Geological Survey 331 



This widely distributed and abundant species is represented in Mary- 

 land mainly by broken specimens, the cephalon and pygidium being the 

 parts which are most frequently found. These were compared with 

 authentic specimens of this species in the office of the State Paleontologist 

 of New York, and found to agree closely in all essential characters. The 

 species is found more commonly in ]\Iaryland in the argillaceous shales 

 of the Hamilton, but also occasionally in the arenaceous shales. The 

 species was reported by Hall and Clarke from the Hamilton shales at 

 Cumberland, Md. (Pal. N. Y., vol. vii, p. 26). 



Length of nearly perfect cephalon, 15 mm.; width, 25 mm. Length 

 of most nearly perfect pygidium, 9 mm. ; width, 15 mm. 



Occurrence. — Romkey Formation, Hamilton Member. East bank 

 Evitts Creek below Wolfe Mill ; on National Road i/o mile west of Tonolo- 

 way Ridge; Licking Creek east of Warren Point; McCoys Ferry ; south- 

 west of McCoys Ferry ; Ernstville; on road east of Pine Hill about 4 miles 

 north of Oldtown. 



Collections. — Maryland Geological Survey; New York State Museum; 

 American Museum of Natural History. 



Phacops cristata Hall 

 Plate XLIII, Figs. 13-15 



Phacops cristata Hall, 1861, Desc. New Sp. Fos., p. 67. 



Phacops cristata Hall and Clarke, 1888, Nat. Hist. New York Paleontology, 



vol. vii, p. 14, pi. vi, figs. 1-31; 16-29; pi. viiiA, figs. 1-4. 

 Phacops cristata Kindle, 1912, Bull. U. S. Geol. Surv., No. 508, p. 107, pi. x, 



flgs. 6-8. 



Description. — This species is distinguished by the following features 

 according to Hall. The annulations of the pygidium are dichotomous; 

 tennination of axis is obtuse, the axial row of spines extend as far as the 

 pygidium, the glabella is strongly protuberant, tuberculations are numer- 

 ous only on the glabella, the genal angles bear stout spines, there are 10 to 

 11 crenulations on each side of submarginal furrow of cephalon, corneal 

 lenses number 23 to 45. 



This species and the related form P. cristata var. pipa are probably 

 the most abundant representatives of the trilobites in this Onondaga 



