PRODUCTUS 117 



fectly distinct lines of growth. The spine bases occur in a rather broad 

 band across the entire valve between the cardinal extremities, just in 

 front of the subgeniculate curvature of the valve, throughout this band 

 rather strong spines occur more or less uniformly at distances of from 3 

 to 5 mm., along the cardinal margin a row of from 5 to 8 spine bases 

 occur on each side of the beak, increasing in size distally and diverging 

 slightly from the cardinal margin, upon the posterior slope a few spine 

 bases are sometimes sparingly scattered but upon the anterior slope they 

 are commonly absent beyond the band already described. 



Brachial valve gently concave throughout the visceral region but curv- 

 ing abruptly into the produced portion anteriorly and laterally, the 

 auriculations scarcely or not at all differentiated from the general sur- 

 face ; mesial fold low, narrow and ill-defined, confined almost entirely to 

 the anterior produced portion of the valve. Surface marked by fre- 

 quently dividing, radiating costse similar to those of the opposite valve, 

 which become more or less obsolescent upon the anterior produced por- 

 tion of the valve, and by similar, wrinkle-like, concentric markings upon 

 the visceral portion, also throughout by fine concentric lines of growth. 

 Spine bases seem to be lacking upon this valve. Internally the cardinal 

 process is rather small and is apparently trifid, extending posteriorly 

 from the cardinal margin into the umbonal cavity of the opposite valve, 

 anteriorly from the base of the cardinal process the median ridge extends 

 nearly to the anterior side of the visceral portion of the valve, the brachial 

 impressions are rather widely separated and extend anteriorly nearly to 

 the edge of the visceral portion of the valve. 



Remarks. This species has been variously identified in the past but it 

 is apparently a well characterized, undefined species. It may be easily 

 recognized by the subgeniculate curvature of the pedicle valve, with the 

 conspicuous band of strong spines stretching entirely around the valve 

 between the cardinal extremities and just in front of the geniculate bend- 

 ing of the valve, and by the row of spines along the cardinal margin. 

 The anterior produced portion of the valve is proportionally elongate, and 

 the visceral cavity between the two valves consequently rather shallow, 

 in one specimen having a width of 38 mm., the depth of the visceral cavity 

 being only 10 mm. 



Horizon. Keokuk ( Crawfordsville beds, Indiana). 



PRODUCTUS MAGNUS Meek and Worthen 

 Plate XV, Figs. 1-8 



1861. Productus magnus Meek and Worthen, Proc. Acad. Nat. Sci. Phil., 



p. 142. 

 1863. Productus Fentonensis Swallow, Trans. St. Louis Acad. Nat. Sci., 



vol. 2, p. 93. 



