PRODUCTUS 123 



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

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



Description. Shell above medium size, about as long as wide, the 

 hinge-line about equaling the greatest width. The dimensions of the 

 holotype, a crushed example showing only the brachial valve with the 

 umbonal region of the pedicle valve, are : length of brachial valve 30 mm., 

 length of pedicle valve 40 mm., greatest width 40 mm. The dimensions 

 of a somewhat distorted pedicle valve are: length from front to hinge- 

 line 28 mm., length from front to greatest extension of umbo 34.3 mm., 

 greatest width 37 mm., convexity 15 mm. 



Pedicle valve gibbous, the anterior slope apparently somewhat more 

 abrupt than the posterior, the umbonal region narrow and strongly pro- 

 tuberant posteriorly, the mesial portion of the valve broadly flattened, 

 the lateral slopes curving abruptly to the margins, the cardinal auricula- 

 tions large, flattened, and rather abruptly differentiated from the lateral 

 slopes ; mesial sinus shallow, rather narrow, and ill-defined laterally ; 

 beak pointed and strongly incurved. Surface marked by rounded, radiat- 

 ing costaB, usually a little less than 1 mm. from center to center, increasing 

 at intervals by bifurcation ; upon the postero-lateral slopes and extending 

 across the cardinal auriculations, rather strong, concentric wrinkles 

 cross the radiating costae; very fine concentric lines of growth mark 

 the entire surface of the valve when it is perfectly preserved. Spine 

 bases are scattered rather generally over the surface of the valve, es- 

 pecially over the median and anterior regions, usually being placed at 

 intervals of from 5 to 10 mm. apart upon the radiating costae, and be- 

 coming somewhat more numerous upon the lateral slopes towards the 

 cardinal extremities. 



Brachial valve apparently gently concave or somewhat flattened in 

 the visceral region, and curving abruptly towards the anterior and lat- 

 eral margins into the produced portion of the valve ; the cardinal auricu- 

 lations rather sharply differentiated from the general surface of the 

 valve. Surface marked by radiating costa3 similar to those of the oppo- 

 site valve, and also by similar, fine concentric markings; the concentric 

 wrinkles of the shell are less conspicuous than upon the pedicle valve; 

 scattered spine bases occur about as in the opposite valve, increasing in 

 number upon the cardinal auriculations. 



Remarks. This species is evidently a rather thin-shelled form, since 

 the specimens observed are usually more or less distorted. The species 

 has not been commonly recognized since its original definition, and has 

 often been considered as a synonym of P. semireticulatus. The holotype 

 of the species is a crushed example upon a limestone slab, the brachial 

 valve and the umbonal region only of the pedicle valve being exposed; 

 extending diagonally outward from each side of the beak is a crowded 



