756 CAMBRIAN BRACHIOPODA. 



BiLLiNGSELLA HiCKsi (Salter MS.) (Davidson). 

 Plate XCVII, figures 7, 7a-b. 



Orthis hichsii (Salter MS.) Davidson, 1868, Geol. Mag., vol. 5, p. 314, PL XVI, figs. 17-19. (Described as a new species; 

 see below for copy.) 



Orthis hichsii Davidson, 1869, British Fossil Brachiopoda, vol. 3, pt. 7, No. 3, p. 230, PI. XXXIII, figs. 13-16. (De- 

 scribed. Figs. 13a and 14a are copied from Davidson, 1868, PI. XVI, figs. 17a and 18a. Fig. 16a is an enlarged 

 drawing of the specimen figured by Davidson, 1868, PL XVI, fig. 19. Figs. 14a, 13a, and 16a are copied in this 

 monograph, PL XCVII, figs. 7, 7a-b, respectively.) 



Orthis hicksi Davidson, Kaysbe, 1883, China, by Richthofen, vol. 4, p. 35. (Discussed in German in the description 

 of "0. linnarssoni." 



Billing sella hicksi (Davidson), Walcott, 1905, Proc. U. S. Nat. Mus., vol. 28, p. 237. (Original description, Davidson, 

 1868, p. 314, copied as below.) 



The original description by Davidson follows: 



Shell small, transversely oval; hinge line shorter than the greatest breadth of the shell; cardinal angles rounded. 

 Dorsal valve semicircular, moderately convex, slightly longitudinally depressed along the middle. Ventral valve 

 convex, deeper than the opposite one. Area triangular, moderately wide; surface of valves ornamented by about 

 ten principal narrow, radiating ribs, with wide interspaces between each pair, in the middle of which is situated a 

 shorter rib. . 



Length about 4, width 5, lines. 



This shell is most nearly related to B. exporrecta. It differs in its more rounded form, fewer 

 radiating ribs, and muscle area of ventral valve. 



The specific name was given in honor of Henr}^ Hicks. 



Formation and locality." — Middle Cambrian : Sandstones in the middle portion of the Menevian at the following 

 localities [Davidson, 1869, p. 230]: (318d) at Porth-y-rhaw; (,318h) at St. Davids; and (318p) at Ninewells; all near 

 St. Davids, South Wales. 



BiLLiNGSELLA HIGHLANDENSIS (Walcott) . 



U 



Plate LXXXVII, figures 4, 4a-c. 



Orthis? highlandensis\NA-LCOTT, 1886, Bull. U. S. Geol. Survey No. 30, pp. 119-120, PL VIII, figs. 3, 3a-b. (Described 

 and discussed as a new species. The specimens represented by figs. 3, 3a-b are redrawn in this monograph, 

 PL LXXXVII, figs. 4c, 4b, and 4, respectively.) 



Orthis? highlandensis AValcott, 1891, Tenth Ann. Kept. U. S. Geol. Survey, p. 612, PL LXXII, figs. 5, 5a-b. (Men- 

 tioned. The figures are copied from those in the preceding reference.) 



Billingsella highlandensis Walcott, 1905, Proc. U. S. Nat. Mus., vol. 28, pp. 237-238. (Described and discussed 

 essentially as below.) 



Shell transversely oval or subrotund. Front broadly rounded and nearly straight in the 

 dorsal valve. On the ventral valve the cardinal line slopes toward the beak at an angle of 

 about 20'^, while in the dorsal valve it is less than 10°. The greatest width is about the middle 

 of the shell. The ventral valve is moderately convex, being most elevated toward the beak, 

 which is slightly arched over to the cardinal margin. 



A dorsal valve associated in the same hand specimen of limestone is more convex than the 

 ventral valve. The cardinal line is shorter than the greatest width of the shell. The median 

 fold is but slightly raised above the general surface, although the front margin has a low, broad 

 arch for the reception of the fold of the ventral valve. 



A slight flattening in the central portion of the ventral valve in some specimens forms a 

 low, broad mesial sinus toward the front margin. 



The surface is marked by concentric lines of growth and fine radiating ribs; on some 

 specimens stronger ribs occur very much as on Billingsella coloradoensis (PI. LXXXV, figs, 

 la-i). Interior casts of the valves show fine, radiating stria; toward the front. In a number 

 of partly exfoliated shells, the shell is shown to be thick and apparently solid, having been 

 replaced by calcite. 



The average-sized ventral valve has a length of 13 mm., with a width of 16 mm. One 

 dorsal valve is 17 mm. in width. 



o Specimens from localities 318h and 318p are included in the collections of the United States National Museum. The type locality is either 

 318d or 318p, Davidson does not indicate which. 



