462 CAJVIBRIAN BRACHIOPODA. 



of the valves, particularly the dorsal. In Oiolus ( Westonia^ euglyphus the traces remaining 

 on the casts indicate a close resemblance to 0. ( TT.) chuarensis (Walcott), and the surface 

 ornamentation is of the same character. Attention has been called to the character of the 

 surface, which is intermediate between that of 0. ( TF.) eUa (Hall and Wliitfield) (p. 456) and 

 0. (F.) aurora (Hall) (PI. XLVI). 



This species differs from Lingulella Imeolata (Walcott) in its surface characters, thick- 

 ness of shell, and usually in outline; it is also usually a larger species, although a few examples 

 of L. lineolata approach it in size. From 0. ( TF.) chuarensis it differs in being much more 

 elongate and proportionately more ovate in outliae. 



Formation and locality. — Middle Cambrian: (74c) "Tonto" sandstone, at the head of Lava Canyon; and 

 (74) sandstones about 300 feet (91.4 in.) above the base of the Tonto group, at the head of Nunkoiueap Valley; both in the 

 Grand Canyon of the Colorado, Arizona. 



Obolus (Westonia) finlandensis Walcott. 



Plate XLVIII, figures 3, 3a-b. 



Obolus (Westonia) finlandensis Walcott, 1902, Proc. TJ. S. Nat. Mus., vol. 25, pp. 611-612. (Described and discussed 

 as below as a new species.) 



General form elongate ovate, with the ventral valve subacuminate and the dorsal valve ovate 

 in outline. Convexity of the two valves moderate. A ventral valve 11 mm. in length has a 

 convexity of about 1.25 mm., and a dorsal valve 8 mm. in length has a convexity of 1 mm. 

 above the plane of the margin. 



The outer surface of the shell is marked by concentric lines of growth with very fine inter- 

 stitial strife. The latter are crossed by fine, radiating strife that are interrupted more or less 

 by the concentric lines of growth. In addition to the concentric and radiating striae there is a 

 series of imbricating lines that are slightly oblique to the longitudinal axis of the shell. These 

 lines terminate at right angles to the margins, curving inward and backward apparently to the 

 opposite side. This type of ornamentation is much like that of several species of Westonia, 

 except that it is somewhat more complicated. 



The cast of the interior of the shell shows the interior surface to have been marked by scat- 

 tered punctse that had a tendency to gather concentrically on the lines of growth. A few rather 

 strong radiating striae also occur outside of the visceral area. 



The shell is rather thick. It is formed of a thin outer layer and several inner layers or 

 lamellffi that are more or less oblique to the outer surface and marked near the front margin by 

 fine radiating striae. The largest specimen has a length of 11 mm., with a width of 7 mm. A 

 dorsal valve of the same width has a length of 8 mm. 



The area of the ventral valve is unknown. That of the dorsal valve is strongly defined and 

 extends well forward on the cardinal slopes. It is marked by transverse striae of growth parallel 

 to the base. 



The only interior markings known are in the dorsal valve. These indicate the course of 

 the main vascular sinus, and the size and length of the median ridge, also the position of the 

 central muscle scars. 



Observations. — The oblique, imbricating lines on the outer surface of this species relate it 

 closely to Oholus ( Westonia) hottnicus (Wiman) and 0. ( TF.) unmani Walcott. The two speci- 

 mens showing the outer shell are unfortunately slightly worn along the median line, so that 

 it is not possible to trace the growth of the oblique, imbricating lines entirely across the shell. 

 In form the shell resembles Lingulella acutangula (Roemer). 



FoEMATiON AND LOCALITY. — Middle Cambrian: (311x) Compact, fine-grained, quartzitic sandstone at Saltvik, 

 Aland Island, Finland, Russia. 



Obolus (Westonia) iphis Walcott 

 ^ Plate XLIX, figures 4, 4a-d. 



Obolus (Westonia) iphis Walcott, 1905, Proc. 1'. S. Nat. Mus., vol. 28, p. 336. (Described as below as a new species.) 



The general form of this shell is well shown by the illustrations. It differs from all other 

 species of Westonia in having a more elongate and acuminate ventral valve and in the presence 



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