BILLINGSELLID^. 741 



Protorthisf hunnebergensis Walcott, Moberg and Segerberg, 1906, Medd. fran Lunds Geol. Faltklubb, Ser. B, No. 2 

 (Aftryck ur K. Fysiografiska Siillskapets Handl., N. F., Bd. 17), pp. 70-71, PI. II, figs. 5, 5a-c. (Described and 

 discussed. Figs. 5, 5a-c, in common with the remaining figures on PI. II of Moberg and Segerberg's paper, 

 were copied from a preliminary photograph of PI. XCV of this monograph.) 



Shell transversely semielliptical, plano-convex. Surface with very fine ribs that increase 

 by interpolation and bifurcation; on some shells bands of slender ribs are delimited by stronger 

 ribs, usually 2 to 5, between 2 more prominent ribs; fine concentric striae give a crenulated 

 aspect to the radiating ribs. Casts of the interior and exterior appear to be minutely papillose, 

 indicating punctse in the shell. 



Ventral valve moderately convex, with the apex curved down to the margin of the area; 

 area and interior luiknown. Dorsal valve flat or very slightly concave between the umbo 

 and margins; apex slightly elevated above the plane of the surface and cardinal line; a median 

 sinus is present in some shells. 



Oiservations. — It is a little hazardous to refer this species to ProtortJiis, as only the general 

 form and surface are known. The nearly plano-convex valves and surface relate it more 

 nearly to ProtortJiis than to PlectortMs, and it does not appear to fall within Leptsena, Rafi- 

 nesquina, or Strophomena. The specimens were collected by Me. Schmalensee in a dark, argil- 

 laceous shale above the Ceratopijge limestone and below the lower graptolite shale. 



The specific name is derived from Hunneberg, Sweden. 



Formation and locality. — Passage beds between the Upper Cambrian and the Ordovician: (390f) Shales 

 between the " lower graptolite slate " and the Ceratopygeliaiestone, at Mossebo, on Hunneberg, western boundary of 

 the Province of Skaraborg, Sweden. 



, Protorthis l^vis Walcott. 



Plate XCIX, figures 6, 6a-b. 



Protorthis Ixvis Walcott, 1905, Proc. U. S. Nat. Mus., vol. 28, p. 283. (Described and discussed as below as a new 

 species.) 



Ventral valve transversely semicircular, moderately convex; surface of cast smooth; area 

 overhanging the hinge line at about 30° from the plane of the margin of the valve. The cast 

 shows a very clearly defined free spondylium. Shell about 6 mm. in width and 4 mm. in 

 length. 



Tills is one of the few representatives of the genus known outside of the Atlantic basin 

 Cambrian fauna. Its smooth surface and incHned area distinguish it from other species of the 

 genus. 



Formation and locality. — Upper Cambrian: (79a) "St. Croix sandstone" in a quarry and ledge 0.5 mile 

 (0.8 km.) southeast of the county courthouse, Menomonie, Dunn County, Wisconsin. 



j Protorthis latourensis (Matthew). 



Plate XCIX, figures 3, 3a-d. 



Kutorgina Zatowrensis Matthew, 1886, Trans. Roy. Soc. Canada, vol. 3, sec. 4, No. 4, pp. 42^3, PI. V, figs. IS, 18a-c. 



(Described arid discussed. None of the specimens represented by figs. 18, 18a-c are figured in this monograph.) 

 Kutorgina latourensis (Matthew), Hall and Clarke, 1892, Nat. Hist. New York, Paleontology, vol. 8, pt. 1, pp. 93, 



95, and 233, PI. IV, figs. 18-20. (Discussed.) 

 Protorthis latourensis (Matthew), Walcott, 1905, Proc. U. S. Nat. Mus., vol. 28, pp. 282-283. (Original description, 



Matthew, 1886, pp. 42-43, copied, and species discussed as 'on p. 742.) 



The original description by Matthew follows : 



Valves narrowly semicu'cular, broader than long, fiat; umbones low; greatest thickness in the posterior third; 

 hinge line shorter than the width of the shell. 



Dorsal valve with a distinct median depression extending from the umbo to the front margin, and with low 

 ridges diverging from the beak toward the lateral third of the front of the valve. Umbo not elevated above the hinge 

 area, which is exceedingly narrow or absent. Hinge line with two shai-p slightly projecting teeth near the umbo 

 (crura?). 



Ventral valve with a narrow median ridge extending two-thirds of the length of the valve toward the front mar- 

 gin; also with a fainter ridge on each side diverging toward the lateral third of the border of the valve; umbo very 



