F. R. Cowper Reed — A New JV. American Trilohite. 361 



diagonal furi-ow crosses each of these fourth pleurge, but is not 

 continued on to the free spine. The separation of this pair of pleuree 

 from the fifth pair is well marked by distinct interpleural furrows. 



The fifth pair of pleurte, which are short and wider towards their 

 extremity than at their base, are directed backwards and slightly 

 outwards, ended in short rounded spines projecting freely beyond 

 the margin. The sixth pair of pleurfe are fused together in the 

 middle line directly behind the axis, but are separated by a well- 

 marked furrow from the preceding pair, which they resemble in 

 shape. They are directed straight iDackwards, and end in short 

 rounded spines of the same size as those of the fifth pair and likewise 

 projecting freely beyond the margin. The strong diagonal furrows 

 of this sixth pair of pleurse are parallel to each other, and run down 

 the centre of each pleura to the base of the spine. 



Measurements. 







ram. 



ngth of specimen 



17-0 



,, head-shield ... 



6-0 



,, thorax 



6-5 



,, pyg-idium 



5-0 



idth of head-shield ... 



14-5 



,, thorax (front eud) 



9-0 



,, pygidium 



8-5 



Affinities. — There has been only one species (0. primus, Walcott) ^ 

 described belonging to this genus, and to this form 0. Beynoldsi 

 bears a very close resemblance. The head-shield offers scarcely any 

 points of difi'erence, but the palpebral lobes of our new form are 

 longer, and the genal spines are also more elongated. The thorax of 

 Walcott's species is unknown. The pygidium of our form differs by 

 its shorter axis not reaching the posterior mai-gin, by the possession 

 of six instead of five pairs of pleura, by their diagonal furrows and 

 by the relative development of their free pointed extremities. Tlie 

 number of segments in the axis is, however, the same, and the freely 

 projecting points of the pleurae with the reduced length of the last 

 pair behind the axis give a general appearance of similarity. 



Though the head-shield shows such distinct and unique features, 

 particularly in the lobation of the glabella, the resemblance of the 

 pygidium to that of several species of Olenoides (0. quadriceps, 

 Meek, O. wahsatcheiisis, Hall & Whitfield, 0. Fordi, Walcott) 

 deserves notice. The pleurae recall those of Paradoxides, while the 

 spiuose rings of the axis remind one of Olenoides (Zacanthoides) 

 typicalis (Walcott) and 0. neoadensis (Meek). 



Oryctocephalus primus (Walcott) is found in the Middle Cambrian 

 Limestone, east of Pioche, Nevada,- but so far as I know the genus 

 has not been recorded elsewhere. 



1 Bull. U.S. Geol. Surv., No. 30 (1886). " Cambrian Faunas of North America," 

 pt. 2, p. 210, pi. xxix, figs. 3, Za: Tenth Ann. Rep. U.S. Geol. Surv., 1888. 

 " The Fauna of the Olenellus Zone," p. 653, pi. xcv, figs. 4, 4a. 



^ Walcott: Bull. U.S. Geol. Surv., No. 30 (1886), p. 210. 



