62 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 53 



1UUS Walcott [1905a, p. 325] from China, but it differs in having a 

 less elongate ventral valve and in its peculiar surface. 



Formation and Locality. — Lower Cambrian: (i) 1,250 feet 

 (381 m.) above Lake Agnes, in the shales of the Mt. Whyte forma- 

 tion [Walcott, 1908a, p. 4], on the north slope of Mt. Whyte, about 

 4 miles (6.44 km.) south of Laggan, on the Canadian Pacific Rail- 

 way, Alberta; and (2) drift block of shale supposed to have come 

 from the Mt. Whyte formation, on the south slope of Mount Bos- 

 zvorth, on the Continental Divide, one inile (1.61 km.) zvcst of 

 Stephen, on the Canadian Pacific Raihvay, British Columbia, Canada. 



OBOLUS SMITHI, new species 



Plate 7, Figures 9 and 9a 



General form broadly ovate, with the ventral valve obtusely acu- 

 minate and the dorsal valve subcircular, slightly transverse; con- 

 vexity apparently moderate, judging from the specimens as they 

 occur slightly flattened out in the calcareous shales. The shell was 

 relatively strong and formed of a number of thin layers or lamellae 

 that, toward the outer edge of the valve, were more numerous and 

 gave a scaly appearance to the margins of the old shells. 



Surface marked by concentric lines of growth and numerous very 

 fine, slightly irregular, undulating, concentric ridges upon which 

 numerous very minute papillae occur, giving the surface, under a 

 strong magnifying power, the appearance of being minutely granular. 



A ventral valve 6 mm. in length has a width of 6.75 mm. A 

 slightly larger dorsal valve 7.5 mm. in length has a width of 8 mm. 



As shown in the cast, the area of the ventral valve is very short 

 and divided by a relatively strongly marked, narrow pedicle furrow, 

 the edges of which were elevated slightly above the general plane 

 of the area. The cast of the interior shows that the visceral area 

 was continued by a slight, narrow median ridge ; the main vascular 

 sinuses extended rather directly forward from the umbo nearly to 

 the front of the shell, separating very gradually and bounding the 

 interior third of the valve. Nothing has been observed of the 

 muscle scars. 



The cast of the dorsal valve shows that it had a very short area 

 that extended well out on the cardinal slopes; that a low central 

 ridge extended a little more than half the length of the shell and 

 was continued by a slight, narrow median ridge ; the main vascular 

 sinuses extend directly and obliquely forward well toward the front 

 of the shell in about the same relative position as in the ventral 



