336 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxviii. 



to Olenellus are indisputably of that genus, 1 am inclined to refer the 

 bowlder and its contained fossils to the Middle Cambrian. The fact 

 that O. ( Wesstonia) hottnica is nearly identical with 0. ( Westonia) 

 Jinlandeni<is of the Paradoxides tessini series of Finland, also points 

 to the Middle Cambrian age of the fauna. 



OBOLUS (WESTONIA) IPHIS, new species. 



This shell differs from all other species of Westonia in having a more 

 elongate and accuminate ventral valve, and in the presence of a marked 

 mesial depression on the dorsal valve. The shell is rather thin and 

 made up of several very thin layers or lamellae. The outer surface is 

 marked by line radiating stride, concentric strife, and lines of growth, 

 and fine more or less undulating, transverse lines that cross both the 

 radiating and concentric lines. The transverse lines appear to be the 

 edges of slightly elevated imbricating lamellae of the shell. 



Formation and locality. — Upper Cambrian and Ordovician. Lower 

 Ordovician Pogonip formation, Hamburg Ridge; also near the BuU- 

 wacker Mine, in the Upper Cambrian Eureka District, Nevada. 



OBOLUS (WESTONIA) THEMIS, new species. 



General form subsemieircular, with the ventral valve subaccuminate 

 and the dorsal valve broadly ovate in outline. Valves rather strongly 

 convex. Surface of the shell marked by strong concentric lines of 

 growth with finer intermediate striae; in addition there are ver}^ fine, 

 irregular, raised, more or less transverse strife that inosculate, form- 

 ing a minutel}^ papillose or granular surface much like that of O. ( IF.) 

 ella. It often occurs that the outer surface has been removed by attri- 

 tion in the sand, so that the shell has a smooth, polished surface. 

 Owing to the condition of preservation, the markings of the inner 

 layers are not preserved. The shell is strong and thick in advance of 

 the center. It is made up of the thin, outer surface laA^er and several 

 inner layers, as lamellas, in the posterior portions that are slightly 

 oblique to the outer surface. After the shell has attained a size of 2 

 or 3 mm., the lamelhe are more oblique to the outer surface and form 

 a thick, strong shell, the outer edges of which often produce a rather 

 rough surface. 



The largest ventral valve in the collection has a length and breadth 

 of 10 mm.; a dorsal valve 10 mm. in length has a width of 11 mm. 

 The onl}^ interior portion of the shell known is on a fragmentary^ ven- 

 tral valve, in which the visceral area does not reach the center, and 

 the main vascular sinuses are about halfwa}^ between the center and 

 the lateral margins of the valve. 



Oh^ervations. — The general form and character of the shell is much 

 like that of 0, lojperi. It differs from the latter in surface characters. 



