RHYNCHOPORA 239 



have been included in the genus Rkynchopora in this volume. The ap- 

 parent absence of any indication of punctate shell structure is op- 

 posed to the inclusion of the present species in Rhynchop&ra, but this 

 feature is likewise very obscure in II. persinuata, having been observed, 

 indeed, in only a few individuals, and even in those it is not always beyond 

 question, while in R. cooper ensis, another closely allied species, the punc- 

 tate shell structure has never been observed. For the present, therefore, 

 the species will be included in Rhynchopora with a query. The species 

 differs from R. persinuata in its somewhat greater proportionate width 

 and consequent coarser plications which are separated by relatively shal- 

 lower and broader furrows. The anterior lingual extension of the pedicle 

 valve is also distinctly concave transversely in the type, giving to the 

 anterior margin of the shell a distinctly emarginate outline, while in 

 R. persinuata this lingual extension is flat and the anterior margin of the 

 shell consequently straight. 

 Horizon. Louisiana limestone. 



RHYNCHOPORA ? PERRYENSIS n. sp. 

 Plate XXV, Figs. 18-21 



Description. Shell small, broadly subovate in outline, usually a little 

 wider than long, the greatest width near the mid-length of the shell, the 

 postero-lateral margins nearly straight and meeting at the beak in an 

 angle of from 105 to 110 degrees, the antero-lateral and anterior margins 

 rounded. The dimensions of a nearly perfect specimen are: length of 

 pedicle valve 10.2 mm., length of brachial valve 9.2 mm., greatest width 

 10.5 mm., thickness 8 mm., width of sinus in front 7.1 mm. 



Pedicle valve convex in the umbonal region, rather narrowly rounded 

 transversely across the median line with the surface gently convex to the 

 antero-lateral margins and curving abruptly to the postero-lateral mar- 

 gins, from the beak to the anterior margin along the median line the 

 surface describes nearly a semicircular curve; mesial sinus originating 

 near the middle of the valve, nearly flat or slightly convex transversely 

 in the bottom, produced anteriorly in a rounded lingual extension of 

 greater or less length; beak sharply pointed and strongly incurved, the 

 apex coming in contact with the umbo of the opposite valve, the delthy- 

 rium hidden by the incurvature of the beak ; plications simple, obsolete 

 towards the beak but originating in the umbonal region, they are low 

 and broadly rounded posteriorly, becoming more angular towards the 

 front, two or three, rarely four, occupy the bottom of the mesial sinus, 

 the sloping sides of the sinus being entirely nonplicate ; upon each lateral 

 slope of the valve are from four to six plications which grow successively 

 smaller towards the cardinal extremities, the last one or two being very 



