NO. 1395. CAMBRIAN BRACHIOPODA—WALCOTT. 263 



beak arches over a hio-h, ))ackward inolinini^- area. Tho dorsal valve is 

 much like the ventral iu form, except that it is h^s.s 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 S mm. The 

 dorsal valve is a little shorter than the ventral. 



This shell is not unlike FltcioTthk indimiola in form and surface 

 characters. It difters in being more convex and in the absence of a 

 sinus or median fold on either valve. 



Formation and locality. — Middle Cambrian. Chang Hsia limestone. 

 Two and three-quarters miles southwest of Yen Chuang, Shantung, 

 China. 



Collection of Mr. Eliot Blackwelder, Carnegie Institution Expedi- 

 tion to China. 



PLECTORTHIS HASTINGSENSIS, 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 interspaces on the ventral 

 valve; concentric ridges and tine strise of growth are a marked feature 

 of the surface. A ventral valve 4 mm. in length has a width of 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 shell-^, and becoming more so 

 as they increase iu size; area low and inclined backward over the hinge 

 line. 



Ohservations. — This species is unlike other described forms in the 

 character of its ribs, with the exception of Plectorthis johaiuiensis^ 

 which it resembles very closely. Doctor Matthew 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. Dr. G. F. 

 Matthew mentions having found fragments of Protorthis or Orthis in 

 the phosphate nodules at Hastings Cove, too imperfect for description.^' 



Formation and locality. — Middle Cambrian. Upper Paradoxides 

 zone. Hastings Cove, Kennebecasis River, at base of Paradoxides 

 zone, Hanford Brook, in limestone and superjacent shale, St. John 

 County, New Brunswick. 



"Trans. Roy. Soc. Canada, 2d ser., Ill, 1897, p. 180. 



