LAMELLIBRANCHIATA. 79 



Pterinopecten Neptunus. 



PLATE VIII, FIGS. 5-7. 



Pleri nnpecten Neptiuiii-', Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations : PI. 8, tigs. .5-7. 



Jan., 1883. 



Shell large, sub-orbicular, moderately oblique (more so in young shells) ; length 

 one-fifth greater than the height ; pallial margins regulai'ly rounded, becom- 

 ing extended posteriorly. 



Valves moderately and nearly equally convex ; very similar in form and 

 surface markings. 



Hinge-line straight, length less than the length of the shell, situated ante- 

 riorly as regards the body of the valve. 



Beaks obtuse, rounded, directed .^lightly forward, nearly erect, not promi- 

 nent. Umbonal region wide and undefined posteriorly, subtending a very 

 obtuse angle. 



Posterior ear much the larger, slightly concave on the margin ; extremity 

 angular. Anterior ear small, separated from the body of the shell by a 

 sulcus ; margin convex, extending obliquely outward from the byssal sinus ; 

 extremity acute. 



Surfiice marked by closely arranged, rounded or sub-angular rays, which 

 increase by intercalation and bifurcation. The ears are marked by simple and 

 smaller rays, which in the right valve are distinctly angular. The rays 

 become obsolete on the umbo. The concentric striae are close, undulating, 

 and in some conditions may have been sharply elevated and lamellose. 



Internal characters not known. 



The specimen, fig. 6 of pi. 8 is 55 mm. in length, 46 mm. in height, hinge- 

 line -88 mm. 



The comparison of this species with P. crenicostatus is given under the 

 description of that species. 



In surface ornamentation this species somewhat resembles P. Vertumnus, but 

 the shell is shorter and less oblique, the hinge-line shorter, and the concentric 

 striae less elevated. 



