BILLINGSELLID^. 737 



extends from the high vertical apex to the frontal edge, is bordered by obtusely rounded edges. Dorsal valve pro- 

 portionally more bulged than in the type form. Sculpture as in Orthis perpasta. 



The outer form strikingly recalls Orthisina; but the pseudodeltidium, the median septum, and the spondylium 

 of the ventral valve are lacking. 



Orthis perpasta var. subquadrata was found in several internal casts and impressions, together with Orthis perpasta, 

 more rarely in graywacke sandstone than in the conglomerate-like, quartzitic sandstone. 



Observations. — -This variety apparently is not constant, as ventral valves occur in the 

 material before me that have the subquadrate form with relatively less convexity than the 

 convex forms of the species perpasta. 



Formation and locality. — Lower Cambrian : Conglomeratic sandstones and graywacke inclusions in the lower 

 conglomerate zone of the Kamenn^ hurka at the following localities [Pompeckj, 1896b, p. 516]: (345i) near Tejfovik; 

 and (345j) at Gross Lohovic, southwest of Skrej; both in Bohemia, Austria-Hungarj'. 



NisusiA (Jamesella) spencei (Walcott). 



Text figure 62; Plate XCIII, figures 7, 7a. 

 Protorthis spencei Walcott, 1905, Proc. U. S. Nat. Mus., vol. 28, p. 285. (Described as below as a new species.) 



This is a strongly marked species, despite the fact that the few specimens that have been 

 found are flattened in the shale. It is distinguished by its rounded, subquadrate outlines 

 and narrow, sharp ribs with strong interspaces, six ribs in a dis- 

 tance of 5 mm. at the front margin. The area of the ventral A^alve 

 has a broad delthyrium with a convex deltidium covering the 

 greater part of it. The interior surface of the shell is finely punc- 

 tate. A flattened ventral valve has a length of 17 mm.; width, 

 18 mm. 



This shell is associated with Nisusia (Jamesella) nautes (Wal- 

 cott). It differs from it in its larger size, sharper ribs, and broader 

 interspaces between the ribs. 



The discovery in the collection of 1907 of a specimen of a 

 ventral valve showing a very perfect area and arched deltidium -A. 



. 1 , , 1 • 1 • 1 j_i £ J. 7-» J j^ • Figure 62. — Nisusia (Jamesella) spencei 



proves that the specimen upon which the reference to Protorthis (waicott). a, a', Exterior of ventral 

 was based had the deltidium crushed so that it was concave, thus vaive and view of cardinal area. 

 causing it to be mistaken for the free spondylium of Protorthis. '^^^ specimen represented is from 



_,, .„ .. ., c-nr-noo c Locality S5o, Middle Cambrian Spence 



The Specmc name is given m honor of Mr. K. S. bpence, of shale, near Liberty, Bear Lake county, 



Evanston Wvomine. Idaho (U. S. Nat. Mus. cat. No. S2435a). 



• FoKMATioN AND LOCALITY. — Middle Cambrian: (S5c and 163) <^ Spence shale member of the TJte limestone [Walcott, 

 1908a, p. 8], about 50 feet {15.2 m.) above the Brigham quartzite and 2,755 feet (839.7 m.) beloiu the Upper Cambrian, in a 

 ravine running up into Danish Flat from, Mill Canyon, about 6 miles (9.6 km.) ivest-southtoest of Liberty and 15 miles 

 {24-2 hra.) west of Montpelier, Bear Lake County, Idaho. 



(llil) About 2,350 feet (716.3 m.) above the Lower Cambrian and 2,050 feet (624.8 m.) below the Upper Cam- 

 brian in the limestone forming Ic of the Marjum limestone [Walcott, 1908f , p. 180], ridge east of 'Wheeler Amphitheater 

 [Walcott, 1908f, Pis. XIII and XV], House Range, Millard County, Utah. 



Nisusia (Jamesella) utahensis Walcott. 



Plate CI, figures 10, 10a. 



Nisusia (Jamesella) utahensis Walcott, 1905, Proc. U. S. Nat. Mus., vol. 28, pp. 255-256. (Described and discussed 

 as below as a new species.) 



Ventral valve transverse, strongly convex; most elevated at the umbo, which is sur- 

 mounted by the upward pointing apex at the edge of the area; area slightly inclined forward 

 from the hinge line; delthyrium large and covered by a convex deltidium. Surface marked 

 by several strong, rounded ribs irregularly alternating with smaller ribs; fine radiating striae 

 occur on the ribs and interspaces. 



a 163 is the tj'pe locality. 

 62667°— VOL 51, pt 1—12 47 



