BRACHIOPODA. 393 



Strophomeua rugoea, var. subteiita.] 



S. incurvata Shepard, of the Trenton, became S. negleda James, of the Hudson 

 River group. S. trentonensis likewise was changed into S. rugosa Blainville, and S. 

 winchelli developed into S. nutans. In the Trenton formation of Minnesota S. septata, 

 a local variation of S. trentonensis, is found, and in the Hudson River group of the 

 Northwest, S. rugosa and S. wisconsinensis are representatives of the latter. 



Formation and locality. Common in the Hudson River group in Ohio, Indiana and Kentucky; 

 Anticosti; Iron Ridge, Wisconsin, and Spring Valley, Minnesota. At Graf, Iowa, and Iron Ridge, Wis- 

 consin, a variety occurs in which the concentric growth lines are very conspicuous and farther apart than 

 in S. rugosa, and this may prove, when more material is at hand, to be specifically distinct. 



Collector. C. Schuchert. 



Mus. Reg. Nos. 8184, (?8185, 8186). 



STROPHOMENA RUGOSA var. SUBTENTA (Conrad Ms.) Hall. 



1841. Strophomena subtenta CONRAD. Fifth Annual Eeport, New York Survey, p. 37 (undefined). 

 1847. Leptcena subtenta HALL. Palasontology of New York, vol. i, p. 115, pi. xxxiB, figs. -9b. 

 1862. Strophomena subtenta BILLINGS. Palaeozoic Fossils, vol. i, p. 132, fig. 109 on p. 130. 

 1873. Strophomena (Hemipronites) plicata (JAMES) MEEK. Palaeontology of Ohio, vol. i, p. 81, pi. vi, 



flgs. 4a, 4b. 



Conrad's specimens of Strophomena subtenta were found in the Hudson River 

 group of the Ohio valley, and can be distinguished from S. rugosa Blainville only by 

 the oblique wrinkling of the shell along the cardinal margins. This character we 

 do not regard as of greater value than varietal. For further remarks see Strophomena 

 trentonensis. 



Formation and locality. Rare in the Hudson River group at Spring Valley, Minnesota. Other 

 localities as for Strophomena rugosa. 



STROPHOMENA PLANODORSATA W. and S. 



PLATE XXXI, FIGS. 8-10. 



1892, April 1. Strophomena planodorsata W. and S. American Geologist, vol. ix, p. 286. 



Shell large, semicircular or subquadrate in outline, concavo-convex, wider than 

 long, greatest width along the hinge-line, or immediately in front of it. Surface 

 with fine, radiating striae, every second or third one somewhat stronger than those 

 intermediate, crossed by exceedingly delicate, closely crowded concentric lines, and 

 towards the anterior margin by a few larger subimbricating lines of growth. Dorsal 

 valve flat or very slightly concave for more than half the length and breadth of 

 the shell from the cardinal margin, thence sloping rapidly towards the lateral and 

 anterior edges. Cardinal area linear, slightly reflexed and centrally occupied by an 

 inconspicuous deltidium. Interior unknown. 



Ventral valve slightly concave, except near the lateral and anterior margins, 

 where it is strongly bent. Cardinal area 5 mm. or more in width in adult examples, 

 more or less elevated, but never very strongly so; deltidium depressed convex, 



