738 CAMBRIAN BRACHIOPODA. 



Only two specimens of somewhat imperfect ventral valves are known of this species. 

 The description is of the best-preserved specimen. The second specimen has a greater num- 

 ber of more regular ribs that increase by interpolation of short ribs. The specimen illustrated 

 has a width of 8 mm. and a length of 4.5 mm. from the apex to the front margin, which is 

 about the distance from the hinge line to the front margin. 



The nearest related species is Nisusia alberta (Walcott), from which it differs in surface 

 ribs, forward inclination of the area, and prominent convex deltidiimi. 



Formation and locality. — Middle Cambrian: (7w) Limestone in Rock Canyon, in the Wasatch Mountains east 

 of Provo, Utah County, Utah. 



NisusTA (Jamesella) sp. undt. Walcott 



Nisusia (Jamesella) sp. undt., Walcott, 1905, Proc. U. S. Nat. Mus., vol. 28, p. 256. (Characterized as below as an 

 undetermined species.) 



This doubtful species is based on an interior cast of a broken ventral valve. The width 

 of the shell is 15 mm., and length 8 mm., with apex broken off. A broad, shallow sinus arches 

 the frontal margin, and narrows toward the umbo. Radiating ribs narrow, about five in a 

 space of 2 mm. 



Formation and locality. — Lower Cambrian: (392a) Limestone at L'Anse au Loup, on the north shore of the 

 Straits of Belleisle, Labrador. 



Genus PBOTOBTHIS Hall and Clarke.^ 

 [t:p6, early; and Orthis.] 



Protorthis Hall and Clarke, 1892, Eleventh Ann. Rept. State Geologist New York for 1891, pp. 273-274. (Described 



as in first two paragraphs below.) 

 Protorthis Hall and Clarke, 1892, Forty-fifth Ann. Rept. New York State Museum for 1891, pp. 589-590. (Copy 



of preceding reference.) 

 Kuiorgina Hall and Clarke [not Walcott], 1892, Nat. Hist. New York, Paleontology, vol. 8, pt. 1, pp. 90-94. (Copies 



Walcott's description, 1886b, p]3. 101-102, and discusses genus, but description and discussion also include 



reference to specimens now referred to Protorthis, Billingsella, Micromitra, Micromitra (Paterina), and Micromitra 



{Iphidella) .) 

 Protorthis Hall and Clarke, 1892, idem, pp. 231-233. (Described and discussed as a new genus. With two omissions 



this reference is copied below.) 

 Billingsella Hall and Clarke, Schuchbrt (in part), 1897, Bull. U. S. Geol. Survey No. 87, p. 158. ' (Characterized 



and discussed. The genus Protorthis is placed as a synonym of Billingsella, and among the species referred 



to the latter genus are species belonging with both Protorthis and Nisusia.) 

 Protorthis Hall and Clarke, Walcott, 1905, Proc. U. S. Nat. Mus., vol. 28, pp. 280-281. (Copies Hall and Clarke, 



1892c, pp. 231-233, and discusses genus as on p. 739.) 

 Protorthis Hall and Clarke, Grabau and Shimer, 1907, North American Index Fossils, vol. 1, p. 211. (Characterized.) 

 Protorthis Hall and Clarke, Walcott, 1908, Smithsonian Misc. Coll., vol. 53, No. 4, PI. XI, and pp. 142 and 147. (Classi- 

 fication of genus.) 



Hall and Clarke [1892c, pp. 231-233] described the species as follows: 



Shells small, transversely subquadrate or semicircular. Hinge line straight, its length being equal to the greatest 

 width of the valves. Valves unequally biconvex, or subplanoconvex, the pedicle valve being the larger. The car- 

 dinal area is narrow on both valves, but is higher on the (ventral) pedicle valve, and is tran.sected by a broad delthy- 

 rium which is closed below by a concave plate apparently produced by the union of the dental lamellae, which are 

 not continued to the bottom of the valve; teeth distinctly developed. In the brachial (dorsal) valve the cardinal 

 area also bears an open delthyrium; the dental sockets are obscure and the crural plates small; the latter appear ti 

 unite and form a low elevation across the base of the delthyrium. Cardinal process absent or rudimentary in all 

 the specunens examined. Muscular markings in both valves extremely obscure. 



a The s^'nonymy for this genus does not give a complete record of the various genera under which the species now included in Prolorthlc wcve 

 formerly placed; it gives only those references in which the genus is discussed or described. To complete the record for the species taken up in 

 the monograph the following mere generic references are listed: 



OrtMs Hartt [1868, p.6«; 1878, p. G44]. Orthisina ? Matthew [1891, p. 131]. 



Orthis V.'alcott [1884a, p. 17). Orlliis (Protottliis) Wysogfirslci [1900, p. 227). 



Kutnrgina Matthew [1886, p. 42]. Protorthis (Billingsella) Grabau and Shimer [1907, p. 



Orthis Matthew [1886, p. 43]. 211]. 



Ortftis Hartt [1891, p. 044]. 



