BILLINGSELLID^. 779 



show the muscular or vascular markings. There may or may not be a mesial depression on 

 either valve. The reference of this species to Eoorthis is made with much reservation. 



Formation and locality. — Upper Cambrian : (81b) "Si. Croix sandstone," near Devils Lake, Sauh County; and 

 (83) "St. Oroix sandstone," near Trempealeau, Trempealeau County; both in Wisconsin. 



EooHTHis DOEis (Walcott) . 

 Plate XCVII, figures 13, 13a. 



Orthis (Plectorthis) doris Walcott, 1905, Proc. U. S. Nat. Mus., vol. 28, pp. 262-263. (Described and discussed as below 

 as a new species.) 



Of this species a ventral and dorsal valve occur in the collection. General form rounded 

 subquadrangular. Ventral valve strongly convex, with the greatest height at the umbo, from 

 which the beak arches over a high backward-inclining area. Dorsal valve much like the ventral 

 in form except that it is less convex and less elevated at the area. 



Surface of both valves with numerous radiating ribs that have an angular summit and an 

 angular depression between them. The ribs increase in number toward the front by interpola- 

 tion. The ventral valve has a length of 7 mm.; width, 8 mm. The dorsal valve is a little 

 shorter than the ventral. 



Observations. — This shell is not unlike Eoorthis indianola in form and surface characters. 

 It differs in being more convex and in the absence of a sinus or median fold on either valve. 



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 Yen- 

 chuang, Sintai district, Shantung, China. 



Eoorthis hastingsensis (Walcott). 



Plate XCIV, figures 3, 3a-c. 



Orthis (Plectorthis) hastingsensis Walcott, 1905, Proc. U. S. Nat. Mus., vol. 28, p. 263. (Described and discussed 

 as below as a new species.) 



Shell transversely subelliptical. Surface with numerous strong, rounded, radiating ribs 

 increasing in number by interpolation; the ribs appear to be broader and with narrower inter- 

 spaces on the ventral valve; concentric ridges and fine striae of g^o^vth are a marked feature 

 of the surface. A ventral valve 4 mm. in length has a width of 6 mm. ; a dorsal valve 6 mm. 

 long is 10 mm. in width. 



Ventral valve strongly convex, most elevated on the umbo, and without mesial fold; apex 

 incurved slightly over the delthyrium; area well defined, and divided midway by a large 

 delthyrium; it is inclined but little from the vertical. 



Dorsal valve slightly convex in young shells, and becoming more so as they increase in 

 size; area low and inclined backward over the hinge line. 



Observations. — This species is unlike other described forms in the character of its ribs, 

 with the exception of Eoorthis johannensis, which it resembles very closely. Matthew [1892, 

 p. 49] describes the latter species as having a very thin shell, and it is found in the Upper Cam- 

 brian at St. John. No interior features have been seen. Matthew [1897b, p. 170] mentions 

 having found fragments of Protorthis ox Orthis in the phosphate nodules at Hastings Cove, too 

 imperfect for description. 



The species derives its specific name from its occurrence at Hastings Cove. 



Formation and locality. — Middle Cambrian : (8 1 and 2m) » Limestone and superjacent shale at the base of the 

 Paradoxides zone [Matthew, lS95a, p. lOS], on Hanford Brook, St. John County; and (2s) limestone in upper part of 

 Paradoxides zone, Hastings Cove [Matthew, 1898b, p. 38], on Kennebecasis Bay, 0.5 mile (0.8 km.) northeast of Torry- 

 burn, on the Intercolonial Railway northeast of St. John, St. John County; all in New Brunswick. 



o 21 is the type locality. 



