BRACHIOPODA. 397 



Strophomena billingsl.l 



species, restricted to the Hudson River group, and takes the place of S. nutans 

 of the Ohio valley, in the deposits of this formation on Anticosti and in Min- 

 nesota. 



Formation and locality. Common in the Hudson River group at Spring Valley, Wykoff and near 

 Granger,, Minnesota: Anticosti. 



Collectors. E. O. Ulrich, W. H. Scofleld and the writers. Also in the collection of Dr. C. H. 

 Robbins, of Wykoff, Minnesota. 



Mus. Reg. Nos. 232, 430, 4077, 8187, 8188. 



STROPHOMENA BILLINGSI n. sp. 

 a b 



FIG. 32. Billings' original illustration of Strophomena recta, a, side view; 6, ventral view: 

 c, portion of face enlarged. 



1862. Strophomena recta. BILLINGS (non Conrad). Paleozoic Fossils, vol. i, p. 130, flgs. 108a-108c. 



Original description: " Semielliptical, both valves nearly flat, hinge-line equal 

 to, a little greater or a little less than, the width; sides somewhat straight for about 

 half the length, and either parallel or slightly converging forwards; all of the front 

 half of the shell uniformly rounded, sometimes only gently convex or somewhat 

 straight in the middle of the front margin. Ventral valve slightly convex in the 

 umbonal regon, and elsewhere flat or gently concave; beak scarcely distinct from 

 the cardinal area, slightly depressed below the umbo; area of medium size, flat, 

 extending the whole length of the shell, forming an obtuse angle of from 110 to 135 

 with the plane of the lateral margin; foramen triangular, width at the base greater 

 than the bight, closed by a convex deltidium which does not quite v reach the hinge- 

 line, but has its lower margin concave. Dorsal valve uniformly very depressed 

 convex or nearly flat, slightly concave at the cardinal angles and with a barely 

 perceptible mesial depression along the middle, which commences very near the 

 beak and extends one-third or one-half the length of the shell; beak very small and 

 minutely elevated above the cardinal edge; area varying in size from less than one- 

 half to nearly equal that of the ventral valve. 



"Surface with fine, rounded, slightly crenulated, radiating striae of different 

 sizes, the smaller coming in by implantation at various distances from the beak. In 

 some specimens the striae are more nearly of one uniform size than in others; at the 

 front margin there are usually four of the larger and four or five of the smaller stride 

 in the width of one line. When the surface is perfectly preserved it is seen to be 



