BILLINGSELLID^. 789 



valve with the strong umbonal cavity, and the radiating ribs increasing in number by inter- 

 polation, appear to sustain the reference. 



The species derives its name from its occurrence near Salta. 



Formation and locality. — Tipper Cambrian : (389 [Kayser, 1876, p. 8]) Sandstone at Salta, Province of Salta; (389a 

 [Kayser, 1876, p. 8]) sandstone at Nevado de Castillo, Province of Salta; (389(1 [Kayser, 1897, p. 280]) at Iruya, 

 Province of Salta; (389c [Kayser, 1897, p. 280]) in conglomeratic sandstone at Ojo de Agua,' Province of Santiago del 

 Est; and (389b [Kayser, 1876, p. 8]) sandstone at Tilcuya, Province of Jujuy; all in Argentina, South America. 



Kayser [1876, p. 9, PI. I, fig. 13] also describes and illustrates the dorsal valve of a shell 

 that he refers to Orihis sp. It suggests Orusia lenticularis. 



EooRTHis TATEi (Etheridge). 



Plate XCVII, figures 15 and 15a. 



Orthis {f)tatei Ethekidge, jr., 1905, Trans. Roy. Soc. South Australia, vol. 29, p. 249, PL XXV, figs. 7 and 8. 

 (Described as below, and discussed as a new species. The specimens represented by figs. 7 and 8 are redrawn 

 in this monograph, PL XCVII, figs. 15 and 15a, respectively.) 



The original description by Etheridge follows : 



Pedicle valve, dorsal margin comparatively straight; ventral and lateral margins rounded, the former nonmar- 

 ginate; umbo small, depressed; surface in the median line moderately convex, the wings rather flattened; sculpture 

 consisting of numerous, thick, sometimes bifurcating radiating costse, which die out, or are only faintly perceptible 

 on the wings or toward the lateral margins of the valves, the surface on these portions being also crossed by very fine 

 concentric lines; by the promLuence of two or three costse on each side of the middle, a flattened space, taking the 

 place of a sulcus, is marked off. 



This species appears to belong to the group of Eoorthis represented by E. remniclia (N. H. 

 Winchell). 



The specific name is given in honor of Mr. Ralph Tate. 



Formation and locality. — Middle? Cambrian: (315b [Etheridge, 1905, p. 249]) Limestone at Wirrialpa, 

 Flinders Range, South Australia. 



Eoorthis thyone Walcott. 



^ Text figures 70A-C. 



Nisusia rara Walcott (in part), 1908, Smithsonian Misc. Coll., vol. 53, No. 3, p. 97, PL IX, fig. 13 (not fig. 13a, which 

 represents a specimen of Nisusia rara) (No text reference. Fig. 13, which is reproduced in this monograph 

 as fig. 70A, was inserted on PL IX ^-n^^ 



represent Nisusia rara in the paper A B C 



referred to, one of the figures repre- Figuke 70.— Eoorthis thyone Walcott. A, Natural cast of a ventral valve, the type speci- 



sentino- Eoorthis thyone was acci- men, showing cast of a pseudospondylium (U.S. Nat. Mus. Cat. No. 52378). B, Natural 



J ^ 1? ■ 1,1% <=^t of ^ dorsal valve (0. S. Nat. Mus. Cat. No. 52377a). C, Cast of interior of dorsal 



dentally mcluded.) valve (U. S. Nat. Mus. Cat. No. 52377b). 



Eoorthis thyone Walcott, 1908, idem, pp. The specimens represented are from Middle Cambrian Marjum limestone, 2.5 miles (4 



105-106, PL X, figs. 7 and 7a. (De- km-) <^^^^ "! Antelope Springs, in the ridge east of Wleeler Amphitheater, House Range, 



scribed and discussed as below as a ™lard County, Utah (fig 70A from Locality 3x and figs 70B and 70C from Locality llq). 



■w- n J -7 Figure 70A was published [Walcott, 1908d, PI. IX, fig. 13] as representing the ventr-al valve 



new species, i igs. 7 and 7a are of NisuMa rara and was given Cat. No. 52295a. As e.xplained in the note under the 



copied in this monograph as figs. first reference in the synonymy this was a mistake. Figures 70B and 700 are copied 



70B and 70C, respectively.) '™" '*^^"^''" tWOSd, Pl. X, figs. 7 and 7a, respectively]. 



In outline and size this species resembles Eoorthis wicTiitaensis (Walcott) (PI. XCIV, figs. 

 1, la-n), but in its sharp, uniform, radiating ribs it differs from that and other species having 

 a somewhat simUar outline. The ribs radiate from the beak and increase in number by inter- 

 polation of new ribs at irregular distances from the beak. Nothing is known of the area of 

 either valve. A cast of the interior of a dorsal valve shows rather large muscle scars. 



A large ventral valve has a length of 8 mm. ; width, 9 mm. ; substance of shell unknown. 



