i-i AXii-noi: v. 

 P. CAI:I-I MI to lla.l.lon. I'l. o7, Bgl 8 



Shell smooth, the lidef meeting al an angli . Ant- 



valve with riirht radiating ridges, not counting the swollen po-t 

 Itonlrrs. Numerous n.n.vnt ri<- miii..r ridges cause these ridges to be 

 rugose. Under iUrfftOQ \\ith nine slits, two 1 -ing very close toget 

 eaves sliort. 



Intermediate valves: central area smooth, with tin.- linos of 

 growth ; no distinct keel. Lateral areas prominent, concentrically 

 rugose, with a beaded ridire aloiiLr tlic anterior border, and, to a less 

 extent, along the posterior border. Under surface with a median hori- 

 zontal rib-like swelling; sutural lamina broad, but not deep ; ju.iral 

 sinus shallow ; one lateral slit ; eaves short. Posterior : valve anterior 

 area so large as to reduce the posterior area to a minimum ; smooth ; 

 umbo minute, nearly terminal. Posterior area merely forms a con- 

 centrically grooved thickening of the posterior border of the valve- 

 Under surface : sutural lamina? as before, but the jugal sinus is com- 

 paratively narrow and deep ; slits and teeth absent ; the posterior 

 border is greatly swollen. 



Girdle closely beset with very minute horny spines. The specimen 

 had been dried when I received it, and none of the longer spines, 

 characteristic of other species, are observable ; but I think I can 

 discern traces of small sutural tufts. 



Color : anterior valve with a median triangular area, with the 

 apex at the umbo, is of a kind of chocolate color, which is variegated 

 with minute zigzag grey lines ; the lateral spaces are of a dark slate 

 color. Intermediate valves: central area: jugum pink; greenish 

 toward the umbo when worn down. Pleura dark greenish-brown, 

 with irregular longitudinal green bands. Lateral areas madder 

 brown, blotched with brown. Posterior valve : anterior area resem- 

 bling the central areas ; posterior border pinkish. Under surface of 

 all the valves pale bluish green ; lamina? of insertion white. Girdle 

 reddish-brown. 



Length 14, breadth 9 mill. ; height 4 mill. (Haddon.) 



Tristan da Cuntm. 



Plaxiphora carpenteri HADDON, Challenger Rep. Polyplac., p. 34, 

 t. l,f. 8; t. 3, f. 8-</. 



The sculpture of the shell, slight as it is, is sufficient to character- 

 ize this species. (Haddon.) 



P. OLAUCA Quoy & Gaimard. PI. 68, figs. 68-72. 



Animal oval, widened at the sides. Valves wide, rounded, little 



