LAMELUBRANCHIATA. 1 2«.i 



PTYCHOPTERIA, Hall. 

 Ptychopteria Proto. 



PLATE Will. FIGS ]-•, 14. 



Ptycltopteria Prvto, Hall. Pal N. V.. vol. v, pt. 1. Plates and Explanations: PL 23, figs. 12, 14. 



Jan., 1883. 



Shell small, rhomboidal ; body narrow-ovate, oblique at an angle of about '■>'> 

 with the hinge-line; length more than one-third greater than the height; 

 ante-byssal margin sub-truncate, rounding into the broad sinus; base broadly 



rounded; posterior end somewhat abruptly curved. 



Left valve regularly convex below, gibbous in the middle and above. 



Right valve unknown. 



Hinge-line straight, length a little greater than the height of the valve, 

 and nearly equal to two-thirds its length. 



Beak at about the anterior third of the hinge, prominent, inclined forward. 

 Umbo abruptly gibbous, subtending an acute angle. 



Anterior end large,* rounded, limited by a broad byssal depression directed 

 backward ; extremity angular. Wing small, narrow-triangular, extending 

 to near the posterior end of the body; margin scarcely concave; extremity 

 obtuse. 



Surface marked by fine, regular, elevated radii, which are less conspicuous 

 on the wing ; also by concentric striae, which are often crowded and lamel- 

 lose, producing a somewhat undulated character of the surface. 



Interior unknown. 



A large left valve has a length of 29 mm., height IS mm., and hinge-line 

 20 mm. A smaller specimen has a Length of 20 mm., height 13 mm., and 

 hinge-line 14 mm. 



This species resembles P. sinuosa, but the anterior end is wider; the wing 

 is smaller and not produced at the extremity, and the radii are coarser. These 



*Iuthe descriptions of the species of Ptychopteria ami Leptodesma, the term auric] ■ ear is 



applicable to the anterior extension as i.. Actinopteria and Leiopteria ami the term anterior end has I n 



used for that portion of tin- shell anterior to the Ivyssal Minis. 



17 



