78 University Geological Survey of Kansas. 



t Productus semireticulatus. Plate X, figs. 2-2d; text fig. 2, f. 



An omit €8 semireticulatus Martin, Petref, Derb., p. 7, pi. xxxn, ff. 1, 2, 



pi. xxxiii, f. 4, (1809). 

 Productus inca d' Orbigny, Voy. dans 1' Amer. Me"rid. Pal., p. 51, pi. iv, 



ff. 1-3, (1842); Derby, Bull. Mus. Comp. Zool., in, p. 280, (1876). 

 Productus semireticulatus Norwood and Pratten, Jour. Acad. Nat. Sci. 



Phil., in, p. 11, (1854); White, 13th Ann. Rep. St. Geol. Ind., p. 125, 



pi. xxiv, ff. 1-3, (1884); etc. 

 Productus setigerus Hall, Geol. Surv. Iowa, i, pt. n, p. 638, pi. xix, f. 3. 

 Productus setigerus var. keokuk Hall, ibid. 



Productus martini A. Winchell, Proc. Acad. Nat. Sci. Phil., p. 4, (1863). 

 Productus magnus Hall and Clarke, Pal. N. Y., vin, pt. i, pi. xvii-a, f. 15, 



(1892). 



Shell large, very convex, broader than long ( measured from 

 the hinge to the front) ; hinge line straight, equal to the great- 

 est width of the shell ; cardinal area very narrow but distinct ; 

 beak prominent, appressed, barely arching around the hinge 

 line. Pedicle valve much inflated, greatly prolonged anteriorly 

 in old individuals. Beak broadening rapidly from its point at 

 the hinge toward the anterior ; ears nearly flat, well defined, 

 separated from inflated portion of the shell by a gentle curve ; 

 mesial sinus beginning well toward the beak and continuing 

 to the anterior margin. Surface marked by radiating costse, 

 and the visceral area is also marked by more or less regular, 

 concentric costie, giving the shell a semireticulated appearance. 

 Sometimes both sets of stride extend over the ears, the concen- 

 tric taking the form of wrinkles, which, together with the bases 

 of stout tubular spines, make the ears appear quite rough. 

 Spines sparsely and irregularly distributed over the costciB of 

 the shell but thickest on the ears ; radiating costre increasing 

 by bifurcation and insertion. The interior of the valve is. 

 marked on the ears, anterior and lateral border by a pitted sur- 

 face. Adductor scars are elongate-elliptical, arborescent, hav- 

 ing their anterior extremities raised, situated centrally in the 

 shell. Longitudinal linear lines or folds are present on the 

 outside of these impressions. The dorsal or brachial valve is 

 strongly concave, visceral region nearly flat, in front of which 

 it curves abruptly downward. A slight indistinct mesial fold 

 is present, correspouding to the sinus of the other valve. Ears 

 and surface markings same as in the other valve, except that 



