PRODUCTUS 115 



1892. Productus semireticulatus Hall and Clarke, Pal. N. Y., vol. 8, pt. 1, 

 pi. 18. fig. 12 (not 11 and 13). 



Description. Shell large, as long or longer than wide, the greatest 

 width near the mid-length, the hinge-line shorter than the greatest width. 

 The dimensions of a nearly complete pedicle valve are: length from 

 hinge-line to front margin 38.5 mm., length from umbonal region to front 

 margin 48 mm., greatest width 47 mm., length of hinge-line 35 mm., con- 

 vexity 29.5 mm. 



Pedicle valve gibbous, arched from the umbonal region to the front 

 margin with the posterior curvature a little more abrupt, the umbonal re- 

 gion rather narrow, conspicuously protuberant beyond the hinge-line, the 

 mesial portion of the valve broadly flattened from the umbonal region to 

 the front margin, the lateral slopes curving abruptly to the lateral and 

 cardinal margins, the auriculations at the cardinal extremities very small, 

 the lateral and anterior margins slightly flaring ; mesial sinus slight, some- 

 times essentially wanting, shallow, and ill-defined laterally when present ; 

 beak pointed, strongly incurved. Surface marked by rounded, radiating 

 costse about 1 mm. or 1.5 mm. apart upon the anterior slope, usually be- 

 coming coarser and more or less coalescent towards the anterior margin, 

 upon the posterior slope the costas increase frequently by bifurcation, the 

 divisions becoming much less frequent upon the anterior slope ; upon the 

 posterior slope concentric, wrinkle-like markings cross the radiating 

 costse, giving to the valve a semireticulate style of ornamentation, these 

 markings are strongest towards the cardinal margin, usually becoming 

 rather faint across the median portion of the valve ; fine but rather strong 

 concentric lines of growth cover the entire surface of the valve when it is 

 not exfoliated. Spine bases are inconspicuous and only sparsely scat- 

 tered over the anterior slope of the valve, but just inside the small auric- 

 ulations upon the lateral slopes of the valve, there is a large group of 

 fine, closely crowded spines. The inner surface of the valve towards the 

 anterior and lateral margins, is thickly covered by rather coarse papillae 

 or tubercles which appear as pits upon the surface of internal casts. 



Brachial valve flattened in the visceral region, more concave anteriorly 

 and laterally and becoming moderately produced with the outer margin 

 of the opposite valve ; a broad, low, ill-defined mesial fold commonly orig- 

 inates near the center of the valve and continues to the anterior margin. 

 Surface marked by radiating costae similar to those of the opposite valve, 

 and in its visceral part by concentric, wrinkle-like markings, the concen- 

 tric lines of growth similar to those of the opposite valve. Spine bases 

 apparently absent upon the specimens observed. Internally the cardinal 

 process is rather small and bifid, projecting posteriorly into the umbonal 

 cavity of the opposite valve, anteriorly from its base a median ridge or 



