300 S. SELLER FAUNA OF THE FERN GLEX FORMATION 



auriculations. Pedicle valve gibbous, beak incurved, the median portion 

 of the valve broadly flattened or depressed in a shallow, more or less 

 broad, rather ill defined sinus, the sides abruptly rounding and dropping 

 away almost vertically to the lateral and cardinal margins. Surface of 

 the valve marked by moderately coarse, rounded, longitudinal costae, and 

 on the posterior side by concentric wrinkles, giving to the shell the 

 typical markings of the semireticulate section of the genus; on its an- 

 terior half the shell is marked by the more or less remotely scattered 

 bases of moderately coarse spines, and on the anterior side of each of 

 these spine bases the longitudinal costse of the shell are somewhat fascic- 

 ulate. Brachial valve gently concave posteriorly, becoming flattened 

 toward the cardinal extremities, rather abruptly curved toward the front 

 to conform with the curvature of the opposite valve, elevated along the 

 median line in a low rounded fold. Surface marked by longitudinal 

 costse similar to those of the pedicle valve, and upon the flatter portion 

 of the valve by concentric wrinkles about equal in strength to the longi- 

 tudinal costse. 



The dimensions of a rather small individual are: Width, 31 milli- 

 meters; length, 28 millimeters; length of hinge line, 25 millimeters; 

 length of shell along the median line, following the curvature of the sur- 

 face, 50 millimeters. 



Remarks. — This species approaches P. burlingtonensis in its charac- 

 ters and has usually been so identified. It differs from that species, 

 however, in the lower curvature of the pedicle valve, in the less conspic- 

 uous mesial sinus of the same valve, which is broader and shallower in 

 this species and sometimes even obsolete; it also differs in the fascicula- 

 tion of the longitudinal plications in their extension anteriorly from the 

 spine bases. The species resembles P. costatus almost more closely than 

 it does P. hurling ton en sis, but may be distinguished by its less con- 

 spicuous auriculations and by the absence of the well defined oblique row 

 of spines which extend from the beak anteriorly at the inner margin of 

 the auriculations of P. costatus, and usually by the less strongly marked 

 surface markings of the shell. 



PBODUCTUS SAHPSOXI n. sp. 

 Plate 12, figures 18-22 



Description. — Shell small, as long or longer than wide, rarely a little 

 wider than long, the hinge line shorter than the greatest width of the 

 shell, auriculations small or almost obsolete. Pedicle valve strongly 

 arched, the beak small and strongly incurved beyond the cardinal line, 



