NO. 5 CAMBRIAN TRILOBITES 369 



limbs rather narrow, extended and marked by a strong furrow 

 within the posterior margin. 



Surface finely punctate. 



Observations. — The generic reference is not entirely satisfactory, 

 but with only the cranidium for comparison, I think we may place it 

 with Dolicliometopus until further data are obtained. The presence 

 of a small occipital spine seems to be indicated by a circular break in 

 the test, but this may be deceptive. A similar break occurs on a 

 specimen of D. hoccar, but we know from an unbroken specimen that 

 only a minute node has been broken away. 



The specimen of D. ? expansus occurs in a compact limestone. It 

 was associated with : 



Billingsella whitfieldi (Walcott) 

 Orusia ? eurekensis (Walcott) 

 Orusia lentictdaris (Wahlenberg) 

 Stenotheca elongata Walcott 

 Agnostus bidens Meek 

 Zacanthoides spinosus Walcott 



Formation and locality. — Middle Cambriaji: (55b) Eldorado 

 limestone ; ^ near summit of west side of Secret Canyon, Eureka Dis- 

 trict [Hague, 1892, Atlas], Eureka County, Nevada. 



DOLICHOMETOPUS PRODUCTUS (Hall and Whitfield) 

 Plate 53, figs. 2, 2a-e, 3, 3a-b, 4, 4a 



Ogygia producta Hall and Whitfield, 1877, U. S. Geol. Expl. 40th Parallel, 

 Vol. 4, p. 244, pi. 2, figs. 31-34. (Original description and illustration 

 of species.) 



Ogygia parabola Hall and Whitfield, 1877, Idem, p. 245, pi. 2, fig. 35. 

 (Describes and illustrates a pygidium which was referred to Bathyu- 

 riscus productus (Hall and Whitfield) by Walcott in 1886.) 



Niobe producta Brogger, 1886, Om alderen af Olenellus zone i Nordamerika, 

 p. 211. (Refers species to genus Niobe.) 



Bathyiiriscus productus Walcott, 1886, Bull. U. S. Geol. Surv., No. 30, p. 

 217, pi. 30, figs. I, la-i (in part). (Describes and illustrates species. 

 The specimens illustrated by figs, i, la-b, ig, and ih are now referred 

 to Dolichometopus anax.) 



Bathyuriscus productus Miller, 1889, North American Geol. and Pal., p. 

 533, text fig. 972. (Brief description and i figure copied from Walcott.) 



Bathyuriscus productus Pack, igo6, Jour. Geol., Vol. 14, p. 297, pi. 2, figs. 3, 

 Za-b. (Mentions occurrence of species in " Pioche " Mountain and illus- 

 trates a cranidium and two pygidia.) 



* Walcott, Smithsonian Misc. Coll., Vol. 53, 1908, p. li 



