I 



NO. 1299. CAMBRIAN BRACHIOPOD A— WALCOTT. 607 



mine whether the thin calcareous crust mentioned by Dr. Matthew is. 

 reall}' the true outer la}'er or simply a thin calcareous deposit. 



The lai'gest specimen of a dorsal valve in the collection has a Icnoth 

 of 15 mm., with a width of 13 mm. The corresponding- ventral valve 

 was probal)l3" 1 or 2 mm. longer. 



(}J)Ker rations. — In the material collected 1)}' Mr. S. Ward Lojxt in 

 11>01 there are some specimens that show the form of the ventral and 

 dorsal valves of this species. The shell is broader and rounder tlian I 

 supposed when studying the material Dr. G. F. Matthew sent mc It 

 is quite distinct from O. (Z.) Jfellus and O. (Z.) conclnnus^y^Mh wiiich 

 I placed it. The interior markings are those of Lingulella^ but it may 

 be that more perfect material would prove it to belong to some other 

 subgenus of Oholw<. 



Formation and locality. — Upper Cambrian, thin calcareous la^'ers 

 in the arenaceous shales at McAdams shore, Escasonie, Cape Breton, 

 Nova Scotia. 



OBOLUS iLINGULELLAj SPATULUS, new species. 



General form of the ventral valve spatulate, the sides sloping from 

 the apex forward with a verv slight curvature to the anterior lifth of 

 the shell, where they pass into the broadly rounded frontal margin. 



Dorsal valve ovate, with the greatest width toward the front. Con- 

 vexity moderate, and about equal in both valves. A ventral valve 9 

 mm. in length has a convexity of about 1 mm. A fragment of the 

 outer surface indicates that the surface was relatively smooth, being 

 broken only by tine, scattered stride of growth. The inner laj^ers show 

 concentric lines, also fine, radiating striae. The interior of the shell 

 was marked by scattered postules, concentric striae, and a few radiating 

 lines. 



The largest v(Mitral valve has a length of 9 mm. and a width of 6 

 mm. A dorsal valve 5 nun. in width has a length of 7 mm. 



The only traces of the vascular system preserved is the median ridge 

 of the dorsal valve, which extends forward to the anterior fourth of 

 the shell. 



Observattons. — This very pretty little shell occurs in abundance in 

 the chocolate-brown sandstone interbedded in the shales just al)ove 

 the massive Tonto sandstone. It is distinct from all other species 

 known to me from the Cambrian rocks of the Grand Cannon region, 

 O. (Z.) cliuarensis occurs in a layer of sandstone .50 ov 60 feet higher 

 up in the section. 



Formation and locality. — Middle Cambrian, Tonto sandstone series, 

 just above massive sandstone near mouth of Bass Canyon, on the 

 south side of the Grand Canyon of the Colorado, southeast of Powells 

 Plateau, Arizona. 



