396 CAMBRIAN BRACHIOPODA. 



When the outer layer of the shell is exfoliated, the inner layers are seen to be marked by 

 numerous fine, rounded, radiating striae in addition to the concentric lines of growth; exceedingly 

 fine, irregular, interrupted strias give it in places a pitted appearance, while in a different light 

 it appears to be granulated, a feature of the surface that seems to be present on all of the inner 

 lamellse ; sometimes the impression given is that the shell is minutely punctate. 



The markings of the interior, so far as known, are rounded radiating striae. The shell is 

 rather thick and built up of a thin outer layer and several inner layers or lamellae that in the 

 anterior portions of the shell are rounded obliquely to the outer surface. 



The largest shell in the collection is a somewhat imperfect dorsal valve 8 mm. in length. 

 A smaller valve, 6 mm. in length, has the same width. A ventral valve 6 mm. in length has the 

 portion about the beak broken away and is a little longer than wide. 



The only trace of the interior of the valves is a partial cast of the dorsal valve. This shows 

 that the anterior lateral muscle scars were situated on the anterior portion of the valve about 

 one-third the length of the shell from the anterior margin. 



Observations. — This species I'esembles in many respects 0. matinalis (Hall), especially the 

 Texan form referred to that species. The material is poorly preserved, but it appears to be 

 clearly distinct from any described species. Its surface characters are like those of Oholus 

 prindlei (Walcott) (PI. XXVII). 



The species is named in recognition of the difficult and persevering work of Mr. S. Ward 

 Loper, curator of the museum of Middlebury College, who made a large collection of fossils 

 under the most adverse circumstances in the mountains of Colorado. 



Formation and locality. — Passage beds between the Upper Cambrian and the Ordovician: (335a) Reddish 

 sandstone on Cement Creek, 3 miles (4.8 km.) north of Hot Springs and 8 to 10 miles (12.8-16 km.) southeast of Crested 

 Butte, Ouray County, Colorado. 



Obolus mcconnelli (Walcott). 

 Plate XXIII, figures 3, 3a (not 3b-d).a 



Lingulella mcconnelli Walcott, 1889, Proc. U. S. Nat. Mus., vol. 11, p. 441. (Described as a new species.) 

 Lingulella macconnelli Walcott, Matthew, 1902, Trans. Roy. Soc. Canada, 2d ser., vol. 8, sec. 4, No. 3, p. 108. (Original 



description copied and species discussed.) 

 Oholus mcconnelli Walcott (in part), 1908, Canadian Alpine Journal, vol. 1, No. 2, p. 244, PI. I, fig. 2 (not fig. 2a, referred 

 in this monograph to Oholus septalis). (No text reference. Fig. 2 is copied in this monograph, PI. XXIII, 

 fig. 3a.) 



General form elongate ovate with the ventral valve subacuminate and rather broadly 

 rounded in front and obtusely rounded posteriorly. Wlaen the dorsal valve is crushed and 

 flattened in the shale it is broadly ovate. As far as can be determined from the somewhat 

 compressed shells the valves were moderately convex. Surface of the shell marked by concen- 

 tric lines of growth and fine, irregular striae that are more or less transverse and apparently 

 imbricating, giving a surface a little suggestive of Obolus (Westonia) aurora (Hall) . Wlien the 

 outer layer is exfoliated the surface of the inner layer is marked by concentric and radiating 

 striae. The interior surface is marked by rather strong radiating striae and scattered punctse. 

 The shell is thick for one of its size. It is formed of a thin outer layer, several thin inner 

 layers, and numerous lamellae in the anterior half of the valves. The only interior vascular 

 markings seen are those of the visceral cavity and main vascular sinuses of the ventral valve. 



Observations. — Since the original description [Walcott, 1889c, p. 441] was written a few 

 specimens have been secured that add a little to the data for the description of the species. 



The broad subtrigonal form represented in Plate XXIII, figure 3 a, occurs on the same slab 

 of shaly limestone with the more elongate shell represented in figure 3. The latter is com- 

 pressed laterally, which makes it appear more elongate and also strengthens the radiating striae. 



A small shell from Big Cottonwood Canyon, southeast of Salt Lake City, Utah, provisionally 

 referred to Lingulella helena (Walcott) (PI. XXIV, fig. 3d), may prove to belong to this species. 



a Figures 3b and 3c represent specimens of Obolus mcconnelli pelias. Figure 3d represents a specimen ol Obolus septalis. 



