430 .CAMBRIAN BRACHIOPODA. 



The interior of the ventral valve shows what api^ears to be a short continuation of the car- 

 dinal area forward into the valve before the slope into the visceral cavity; it is as though an 

 area with Unes of growth were added to the internal area of the ventral valve of ETkania deside- 

 rata (Billings) (PI. LI, fig. 1). The front margin of the area merges in 0. (F.) perfectus into 

 the tiiicker shell back of the visceral cavity, much as in 0. (,F.) hellulus (Walcott). The pedicle 

 furrow extends forward from the posteiior margin across the true area and its anterior exten- 

 sion to the visceral cavity. The visceral area is bordered by two ridges that diverge from the 

 sides of the pedicle furrow and extend forward about one-third the length of the valve; these 

 ridges widen toward the front, and where they terminate there appear to be two or three 

 minute muscle scars corresponding to the outside and middle laterals and central scars of 

 Obolus; outside of the ridge there is a furrow that was probably occupied by the main vas- 

 cular canal, and beyond, two narrow, elongate spaces in which the transmedian and anterior 

 lateral muscle scars appear to be situated; all the furrows head back against the thickened 

 shell in front of the cardinal area; the surface of the interior of the valve is marked by con- 

 centric Unes and very fine radiating striae. 



The dorsal valve (PI. XLIII, fig. 10) has a short strong median ridge in fi'ont of the car- 

 dinal area, and well toward the center of the valve a narrow sharp median ridge; on each side 

 of the latter where it begins posteriorly a small oval muscle scar (central h) occurs, and at its 

 anterior end two elongate oval scars (anterior laterals j) that are larger than the centrals; 

 on the tlnckened posterolateral portions of the valve, two small muscle scai's (transmedian 

 and outside and middle laterals, 1 and k) occur close to the outer margin. The surface of the 

 visceral cavity is smooth, but in front of it the minute. irregular vascular markings are very 

 ornate ; a few radiating striae also occur. 



The two interiors described are unusually distinct; usually the various parts and scars 

 are more or less obsciu'e. 



Tliis species approaches 0. (Fordinia) gilherti Walcott more nearly than any other species 

 of the genus. It differs in the presence of the sinus in both valves; in being less convex; in 

 its less pointed beak; and in its strongly marked interior. It occurs over 1,000 feet higher 

 up in the section of the Mddle Cambrian limestones than 0. (F.) gilberti. The interior of its 

 ventral valve is somewhat hke that of 0. (F.) hellulus (Walcott) (PI. LI, fig. 3a), but it differs 

 from that in having a cardinal area in both valves that has not been merged into the internal 

 cardinal area. 



Formation and locality. — Middle Cambrian : (30n and 30n') "■ About 3,750 feet (1,143 m.) above the Lower Cam- 

 brian and 650 feet (198 m.) below the Upper Cambrian in the shaly limestones forming Ic of the Weeks limestone 

 [Walcott, 1908f, p. 175]; and (30o) about 3,950 feet (1,204 m.) above the Lower Cambrian and 450 feet (137.2 m.) below 

 the Upper Cambrian in the shaly limestones forming lb of the Weeks limestone [Walcott, 1908f, p. 178]; both on the 

 north side of Weeks Canyon, about 4 miles (6.4 km.) south of Marjum Pass, House Range [Walcott, 1908f, PI. XIII], 

 Millard County, Utah. 



LINGULOBOLUS Matthe-w,& subgenus of OBOLUS. 



[Lingula and Obolus.] 



Linguloholus Matthew, 1895, Trans. Roy. Soc. Canada for 1895, 2d ser., vol. 1, pp. 260-261. (Described and discussed 



as a new genus.) 

 Sphxrobolus Matthew, 1895, idem, p. 263. (Described and discussed as a provisional new genus.) 

 Obolus (Linguloholus) (Matthew), Walcott, 1901, Proc. U. S. Nat. Mus., vol. 23, p. 683. (Characterized as a subgenus.) 

 Obolus (Linguloholus) (Matthew), Walcott, 1908, Smithsonian Misc. Coll., vol. 53, No. 4, PL XI, and pp. 142 and 144. 



(Classification of subgenus.) 



Differs from typical Oholus in the strongly arched and thick valves, and the surface marked 

 by subimbricated, wavy, concentric fines and strife of growth. 



a sOn is the type locality. 



& The synonymy for this subgenus does not give a complete record of the various genera under which the species now included in Linguloholus 

 were formerly placed; it gives only those references in which the genus is discussed or described. To complete the record the following mere generic 

 references are listed: 



LinguUllaf Billings [1872b, p. 468; 1874, p. 67; I Oholus {Linguloholus) Walcott [1898b, p. 327). 



1882, p. 15]. Linguloholus Grabau [1900, p. 621]. 



LiTigulepis Walcott [1889a, p. 381]. I Sphxroholus Grabau [1900, p. 622]. 



