PRODUCTUS 125 



are developed which are either obsolete across the mesial portion of 

 the valve or are much reduced in strength; the entire surface of the 

 valve marked by very fine, but well-defined concentric markings; when 

 partially exfoliated the shell substance is seen to be rather coarsely 

 but closely punctate, the punctations being more closely crowded upon 

 the summits of the costae than in the intercostal furrows; spine bases 

 apparently absent or very sparsely present upon the main portion of the 

 valve, becoming more abundant towards the anterior and lateral margins, 

 with a rather closely crowded group upon each auriculation. Internal 

 characters not observed. 



Brachial valve concave throughout, produced anteriorly nearly in con- 

 tact with the opposite valve, the auriculations at the cardinal extremities 

 distinctly differentiated, the visceral cavity between the two valves 

 rather deep. Surface marked by radiating costae similar to those of 

 the opposite valve but somewhat finer, and by concentric, wrinkle-like 

 markings which are somewhat finer but more uniformly developed 

 than those upon the posterior portion of the opposite valve; the fine 

 concentric markings similar to those of the opposite valve. Spine bases 

 confined chiefly to the auriculations and along the hinge-line, sparsely 

 scattered or apparently absent from other portions of the valve. 



Remarks. This species has not been generally recognized since its 

 original definition by Norwood and Pratten, probably because of the 

 very unsatisfactory illustration of the species which was published by 

 those authors. The shell is a common one in the Salem limestone and 

 has been identified as P. burlingtonensis and P. gallatinensis by 'Beede. 

 The species differs from P. burlingtonensis in its smaller size, its finer 

 costae, the more pointed umbonal region, the obsolescent character of 

 the concentric wrinkle-like markings upon the median portion of the 

 posterior part of the pedicle valve, and in the absence of a median 

 sinus in the pedicle valve. In the strong, concentric, wrinkle-like mark- 

 ings of the shell upon and adjacent to the auriculations and their nearly 

 or complete absence across the median portion of the pedicle valve, the 

 species resembles P. ovatus, but the radiating costae are much stronger than 

 in that species and they lack the wavy direction. The punctate char- 

 acter of the shell in this species, which is frequently shown in partially 

 exfoliated specimens, has not been observed in any other species here 

 described. 



Horizon. Salem limestone. 



