OLENELLUS AND OTHER GENERA OF MESONACID.E 323 



Couiifv; (51) in thin layers of limestone interbedded between shales 

 and layers of sandstone of the Prospect Mountain formation, west 

 side of summit of Prospect Mountain, Eureka District, Eureka 

 County; and (ip) limestones of No. 2 of the Silver Peak Group, 

 Barrel Spring section [Walcott, igoSc, p. 189], about 2.5 miles 

 (4 km.) south of Barrel Spring and .5 mile (.8 km.) east of road, 

 Silver Peak Quadrangle. Esmeralda County ; all in Nevada. 



(176 and 178a) in arenaceous shales apparently lying between 

 massive limestones carrying .4rcIi<uoc\athus, south end of Deep 

 Spring Valley, about 20 miles (32 km.) east-southeast of Big Pine in 

 Owens \"alley ; (i4p) quartzitic sandstones near Resting (Fresh 

 Water) Springs, which is in the southwest corner of T. 21 N., R. 

 8 E., on the Armagosa River, Inyo County ; and ( 14I) sandstones 

 about 800 feet (244m.) beow massive blue limestones [see Walcott, 

 1908^^ p. 187] in pass through Kingston Range, 15 miles (24 km.) 

 east of Resting Springs ; all in California. 



Fragments of an Olcnclhis with a strong marginal border about 

 the cephalon similar to that of OlencUiis frcmonti occur in (593) 

 a compact sandstone 2.5 miles (4 km.) west of Siam and 7 miles 

 (11 km.) northeast of Cadiz, on the Atlantic and Pacific Railway, 

 San Bernardino County. California. 



OLENELLUS ? GIGAS Peach 



Plate 40, Fig. i 



Olencllus gigas Peach, 1894, Quart. Journ. Geol. Soc. London, Vol. 50, 

 p. 666, text fig. i, p. 667. (Described essentially as below. The speci- 

 men from which text figure i was drawn is reproduced in this paper, 

 pi. 40, fig. I.) 



Of this species only fragments of a large cephalon are known. 

 One of these is illustrated by fig. i. Of this and several other 

 fragments Dr. Peach tells us that the cephalon is 



Much wider compared with its depth than in O. lapZi'orthi and O. rcticu- 

 latus. It is further distinguished from the latter by its broad margin and strong 

 genal spine. The ornamentation is readily seen, even with the unaided eye. As 

 stated in the former paper, the pattern of the reticulation is more elongated on 

 the margins and spines than on the general surface, but this applies equally to 

 all the species of Olcnellus. 



Portions of cheeks and genal spines of individuals nearly as large as the 

 above, on which the pattern of the ornamentation is much smaller proportionally 

 to their size, occur in the collection. 



Measurements. — Length of head-shield, 52 mm.; breadth of head-shield, 

 106 mm. = 4H inches. 



