BEACHIOPODA. 399 



Strophomena emaoiaUl.] 



and short septum, which bifurcates anteriorly. Near the anterior margin of the 

 posterior pair of scars two other ridges arise, making four in all, probably the main 

 trunks of the vascular system. Very small genital spaces indicated outside the 

 muscular scars and in front of the crural plates. 



Ventral valve somewhat deeper than the other, evenly convex, or with a broad, 

 shallow sinus near the anterior margin. Hinge teeth prominent and joining the 

 outer elevated margin of the short, suboval, muscular area. This is centrally divided 

 by a low ridge, separating the two pairs of adductor and diductor scars. 



This species is of the type of S. sinuata (James) Meek.* S. scofieldi can readily be 

 distinguished from the latter by its smaller size and greater number of strise, having 

 about sixty. The profound fold and sinus, greater size, and less numerous striae of 

 S. sulcata de Verneuil,| will distinguish it from S. scofieldi. Another related species is 

 S. cardinalis Whitfield.J The more elevated cardinal area, very convex dorsal valve 

 and greater width of the shell, distinguish this form from S. scofieldi. 



Formation and locality. Rare near the base of the Galena shales at Minneapolis and St. Paul; 

 common in association with Clitambonites diversa at several localities south of Cannon Falls, Minnesota. 

 A single specimen of it has been collected near the top of the "Lower Blue beds" north of Beloit, Wisconsin. 



Collectors. W . H. Scofleld and the writers. 

 Mus. Reg. Nos. 8193-8195. 



STROPHOMENA EMACIATA W. and <V. 



PLATE XXXI, FIGS. 2224. 



1892, April 1. Strophomena emaciata W. and S. American Geologist, vol ix, p. 287. 



Shell small, depressed, biconvex, semicircular in outline; hinge-line usually 

 somewhat smaller than the greatest width of the valve. Surface marked by 

 numerous angulated striae, increasing in number by interpolation, having from 

 sixty to seventy-five of the large and small ones along the anterior margin. 



Ventral valve depressed-convex, subangulated medially, greatest point of eleva- 

 tion about mid-length. Cardinal area narrow, less than 1 mm. in width, strongly 

 elevated, with a very convex, apically-perforated deltidium, which is somewhat 

 wider than long and excavated for the reception of the chilidium. 



Dorsal valve slightly convex, with or without a shallow sinus, having its origin 

 near the beak and rapidly widening to the anterior margin, which is more or less 

 sinuous, according to the depth of the medial depression. Cardinal area linear, with 

 a short, broad chilidium partially covering the cardinal process. Interior unknown. 



This little species was at first regarded as the young of some form of Stropho- 

 mena. There are two species associated with it S. scofieldi and S. trentonensis. If 



* Pal. Ohio, vol. 1, p. 87, pi. V, figs. 5a 5f . 



+ Ibidem, p. 85, pi. V, figs. 4a-4e. 



tOeol. of Wise., vol. iv, p. 261, pi. xii, figs. It, 10. 



