CAMBRIAN TRILOBITKS — WAIXOTT 33 



Hypostoina strongly convex, elongate, strongly rounded at the 

 base, narrowing toward the broadly rounded posterior margin ; 

 border slightly flattened, with a rounded edge; this edge is arched 

 slightly upward on the sides at about the posterior third of the 

 length of the hypostoma ; a shallow furrow crosses the posterior end 

 of the convex body a short distance in front of the posterior margin 

 and subparallel to it ; the alate lateral limbs are subtriangular in out- 

 line and slightly convex. The surface is marked by fine, irregular, 

 elevated lines that are subparallel to the rim on the margin and 

 roughly concentric on the body. An hypostoma 26 mm. in length 

 has a width of 28 mm. at its base, 15 mm. at the arches in the margin 

 or at the posterior third ; convexity at center, 5 mm. 



The above-described hypostoma is associated with this species, 

 Neolenus superhus, and a less convex hypostoma which is referred 

 to the latter species. 



Observations. — This large species and the associated Neolenus 

 supcrbus appear to mark the extreme development in size of species 

 of Neolenus and its latest occurrence in Cambrian time. Fragments 

 of both species are abundant at one locality, and a few entire speci- 

 mens have been found. It is the largest of the Cordilleran Cam- 

 brian trilobites, some of the partially entire specimens indicating a 

 length of 160 mm., width 83 mm. 



The most nearly related species is Neolenus superhus, from which 

 Neolenus iniiatus differs in having an inflated glabella, a longer 

 pygidium, and in minor details of the pleurae of the thoracic seg- 

 ments, pygidium, and cephalon. The inflated glabella, long pygi- 

 dium with ten rings and spinose terminations of the thoracic pleurae, 

 separate it from Neolenus serratus (Rominger),^ the type of the 

 genus. The latter also has a granular surface and falcate termina- 

 tions to the pleurae of the thoracic segments, and the faunal horizon 

 of A^ serratus is 1,900 to 2,125 feet below that of N. inflatus. 



Formation and Locauty. — Middle Cambrian: 1,895-2,140 feet 

 (605-653.8 m.) below the Upper Cambrian and about 2,000 feet 

 (609.6 m.) above the beds containing Zacantlwides typicalis Walcott 

 and Bathyuriscus hozvelU Walcott, the horizon which is correlated 

 with the horizon carrying Neolenus serratus (Rominger) in British 

 Columbia," in thin-bedded limestones of the ]\Iarjum formation, in 

 ridge on east side of Wheeler Amphitheater, east of Antelope 

 Springs, House Range, Millard County, Utah, U. S. A. 



^ Ogygia serrata Rominger, 1887, Proc. Acad. Nat. Sci. Philadelphia, p. 13. 

 'This British Columbia horizon is given in detail in the Formation and 

 locality of Burlingia hectori. 



