BILLINGSELLID^. 



783 



Orthis (Plectorthis) linnarssoni (Kayser), Walcott, 1905, Proc. U. S. Nat. Mus., vol. 28, p. 266. (Original description 

 copied and species discussed as below.) 



The original description by Kayser follows: 

 Shell semielliptical in outline, broader than long, with hinge edge straight, corresponding to the greatest breadth 

 of the shell. Large (ventral) valve moderately convex. Small (dorsal) valve slightly arched, with a sinus which devel- 

 ops at the umbo and grows quite broad and deep toward the edge. Umbo of ventral valve small, area very low. 

 Surface of shell covered with rather sharp ribs, exceedingly variable in strength, separated by naiTow furrows. By 

 reason of repeated splitting, which begins close to the umbo, the ribs appear more like bundles of ribs. On the matrix 

 these bundles appear as broad, obtuse-angled folds, which, owing to repeated marginal splitting in even a higher 

 degree than on the shell itself, appear as bundles of ribs of very unlike strength. 'When the surface is well preserved, 

 a delicate concentric growth striation is perceptible. 



Kayser [1883, p. 35] compares this shell with "Orthis liiclisi" Salter and "0. exporrecta" 

 Linnarsson, on account of the surface characters. It does not appear to be very closely related 

 to either species, but it is in many respects allied to Eoorthis desmopleura (Meek) and E. 

 mchitaensis (Walcott). 



The specific name is given in honor of Dr. J. G. O. Linnarsson. 



Formation and locality. — Upper Cambrian: (C64) Upper limestone member of the Kiulung group [Black- 

 welder, 1907a, pp. 37 and 42 (first list of fossils), and fig. 10 (bed 20), p. 38], 2.7 miles (4.3 km.) southwest of Yenchuang, 

 Sintai district; and (C67) stream gravels used in making the railroad grade 0.33 mile (0.5 km.) west of the west 

 city gate at Tsinan; both in Shantung, China. 



(332a) [Kayser, 1883, p. 34] Taling, Liaotung, China. 



>-' Eoorthis newberryi Walcott. 



Text figures 69A-D. 



Eoorthis neivherryi Walcott, 1908, Smithsonian Misc. Coll., vol. 53, No. 3, p. 105, PL X, figs. 6 and 6a. (Described 

 and discussed as below as a new species. Figs. 6 and 6a are copied in this monograph as figs. 69B and 69D.) 



Shell transversely subelliptical, with the cardinal extremities obtusely angular; valves 

 moderately convex, with the hinge line a little shorter than the greatest width of the valves. 

 The only ventral valve in the collection show- 

 ing a mesial fold (fig. 69A) is a small exfoli- 

 ated shell that is somewhat doubtfully referred 

 to the species. Two large valves, one of which 

 is illustrated by figure 69B, have the posterior 

 margin extended beyond the hinge line, with a 

 short incurved beak; a broad, shallow median 

 sinus begins in front of the umbo and widens 

 to nearly one-third of the width of the valve 

 at the frontal margin. On a shell 5 mm. in 

 length the sinus is very shallow; area un- 

 known. The dorsal valve is almost uniformly 

 convex and without a mesial sinus or fold ; the 

 front margin arches upward a little to provide 

 for the extension of the margin of the ventral 

 valve caused by its broad median sinus; beak 

 minute and marginal; area unknown. . 



Surface marked by concentric lines and 

 ridges of growth and small, rounded, radiating 

 ribs, with two or three smaller ribs between 

 each two larger ridges. The shell structure is 

 fibrous and impunctate as far as can be de- 

 termined from the material available for study. The largest ventral valve has a length of 14 

 mm.; width, 18 mm. A dorsal valve 15 mm. in length has a width of 18 mm. 



Observations. — In form this species resembles some species of Eoorthis remnicha (Winchell) 

 (Pis. XCI, XCII), but in surface characters it is quite unlike any of them. 



Figure 69. — Eoorthis newberryi Walcott. A, Partly exfoliated ventral 

 valve (U. S. Nat. Mus. Cat. No. 52350a). B, Ventral valve, the type 

 specimen, preserving some of the surface characters (U. S. Nat. 

 Mus. Cat. No. S'lSSOWf"- C,.Small exfoliated ventral valve (U. S. 

 Nat. Mus. Cat. No. 52350b)..1 D, Partly exfoliated dorsal valve (U. S. 

 Nat. Mus. Cat. No. 5235011). 6 

 The specimens represented are from Locality 54c, Upper Cambrian 



limestone of the St. Charles formation, in Blacksmith Fork Canyon, 



east of Hyrum, Cache County, Utah. Figures G9B and 69D are copied 



from Walcott [1908d, PI. X, figs. 6 and 6aJ. 



