92 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 75 



The lateral portions of the pygidium are flat, tapering off to ter- 

 minate in two long spines on each side. These spines appear to be 

 the extension of two very broad and furrowed pleurae, fused together 

 by the flat areas between. 



Observations. — A preliminary review has recently been made in 

 connection with the erection of the genus Holteria, of the related 

 genera. It was ascertained that all of the species previously referred 

 to Olenoides (Bull. U. S. Geol. Surv. No. 30, 1886, pp. 180-190) 

 are not congeneric with the genotype, of which only the single 

 specimen originally described has ever been found. This fragment 

 is made distinct by the course of the pleural furrows. It might well 

 be that additional material, if it could ever be found, would prove 

 this specimen to be erratic and not typical. The species of Olenoides 

 all fall quite readily into Neolenus and Kootenia. The cranidia of 



Fig. 13. — Holteria prohlematica (Walcott). 

 Side outline of the cranidium illustrated in figure 17, plate 15. 



the 40 or more species of Kootenia and the dozen or more species 

 assigned to Neolenus, together with those assigned to Holteria, form 

 an almost unbroken series from the one extreme to the other and in 

 the absence of the distinctive pygidia could well be retained in one 

 genus. The pygidia, however, are quite distinct in plan. Holteria 

 has a well-fused pygidium with two spines arising from a flat border 

 on either side. Neolenus lacks the flat border, has the individual 

 pleurae separate enough to be readily distinguishable and from three 

 to nine spines on either side. Kootenia is distinguished by the fusion 

 of the pleurae to the extent that the boundary between them is only 

 rarely discernible, and then with great difficulty. The pleural fur- 

 rows, as in the foregoing genera, are quite deep. Kootenia has visually 

 four or five spines to a side, but they may vary in length from mere 

 scallops to long, heavy spines equal to the length of the pygidium. 



Genotype. — Ogygia ? prohlematica Walcott. 



Range. — Upper Cambrian: Great Basin, Nevada. 



