PRODUCTUS 107 



monly stronger towards the cardinal margins, giving to this portion of 

 the valve a decidedly semireticulate appearance; the entire surface, 

 when well preserved, marked by fine concentric lines of growth. Spine 

 bases usually inconspicuous, sometimes apparently absent, when present 

 they are rather coarse and occur almost entirely upon the anterior and 

 lateral slopes of the valve with occasionally one or more upon each 

 auriculation. 



Brachial valve flattened in the visceral portion with the auricular 

 portions only slightly differentiated, becoming more concave anteriorly 

 and laterally and with the marginal produced region curving rather 

 abruptly to conform with the anterior and lateral portions of the oppo- 

 site valve ; mesial fold, when present, originating posterior to the middle 

 of the valve, it is low, broad and illdefined laterally, not infrequently 

 absent. Surface marked by radiating costas similar to those of the oppo- 

 site valve, and in the visceral portion by well defined, concentric, wrinkle- 

 like markings which make it distinctly semireticulate. Internally the 

 cardinal process is rather short, subtriangular in form with a median 

 groove which does not divide it into two distinct lobes ; it projects poster- 

 iorly into the umbonal cavity of the opposite valve ; other internal char- 

 acters not well preserved. 



Remarks. This species resembles P. burlingtonensis in general form 

 and size, but it differs from that species in the lower curvature of the 

 pedicle valve, and especially in the absence or slight development of 

 the mesial sinus of the pedicle valve. The fasciculate arrangement of 

 the plications anterior to the base of surface spines upon the anterior 

 slope is also a character which differentiates the species from P. 

 Ijurlingtonensis, although it is a character which is not uniformly present. 

 The species differs from P. costatus of the Pennsylvanian faunas, in the 

 smaller auriculations and in the absence of the row of spine bases, which 

 in that species marks the inner margin of each auriculation. 



Horizon. Fern Glen formation and Pierson limestone of the Kinder- 

 hook. 



PRODUCTUS ARCUATUS Hall 

 Plate XIII, Figs. 1-8; ?9-12 



1858. Productus arcuatus Hall, Geol. Iowa, vol. 1, pt. 2, p. 518, pi. 7, 



figs. 4a-b. 



1870. Producta arcuata Winchell, Proc. Am. Phil. Soc., vol. 11, p. 250. 

 1883. Productella arcuata Hall, Rep. N. Y. State Geol., for 1882, pi. (17) 



48, figs. 31, 32. 

 1888. Productus arcuatus Herrick, Bull. Sci. Lab. Denison Univ., vol. 3, p. 



31, pi. 3, fig. 18. 

 1892. Productella arcuata Hall and Clarke, Pal. N. Y., vol. 8, pt. 1, pi. 17 ; 



figs. 31, 32. 

 1894. Productus arcuatus Keyes, Mo. Geol. Surv., vol. 5, p. 40. 



