48 PPJMORDIAL PEinOD. 



Sui-fhce apparently smooth but the condition of the specimen is such 

 that this character is not clearly shown. Remainder of the body unknown^ 

 the only specimen discovered consisting of a well-preserved head alone. 

 Associated with it, however-, the spinous extremity of a pleura was found 

 that possesses the characteristics of similar 25arts of OleneUus, and which 

 probably belonged to an individual of this species. 



This sj)ecies is apjDarently related to 0. Tliompsoni Hall, from rocks in 

 Northern Vermont refen-ed to the Potsdam epoch, where it is associated 

 Yfi\\\ 0. Vermontcma ; but it differs in general outline and proportions, and 

 also in many details^ as shown by comparison with the figiu-es and original 

 description of that species by Professor Hall. The frontal lobe of the 

 glabella in 0. HoiveUl is wider than those behind it, instead of being- nar- 

 rower than the hinder ones, as they are represented to be in 0. Tliompsoni. 

 The details of the exterior and posterior raised margins are different, and 

 the postero-lateral spines are not proportionally so strong in our species as 

 they are represented to be in that on^. The occipital furrow in ours does 

 not extend so distinctly across the glabella as it does in 0. Thompsonl, and 

 the occipital lobe is proportionally wider, and extends farther backward than 

 it does in that species. It is also related to 0. Gilheiii, but differs in gen- 

 eral proportions of the head, the details of the exterior and • posterior bor- 

 ders, and in the pi'oportional size of the different lobes of the glabella. 



As the genus OleneUus is held by geologists to mark a distinct and 

 characteristic horizon in American strata, its discovery in that distant 

 locality is peculiarly valuable and interesting. It is also an interesting and 

 significant fact that the two species here described respectively represent in 

 their specific characters the two originally-described species of the genus 

 found associated in the Primordial rocks of Vermont and Canada, as these 

 are found associated in rocks of the same period in Nevada. 



The specimens from which the descriptions of the two species of 

 OleneUus herein recorded were made are the same that were used by Mr. 

 Meek in his original descriptions and naming of the species. 



Position and localiUj. — Strata of the Primordial period, and probably 

 of the Potsdam epoch, Pioche, Nevada. 



