874 PELECYPODA. [Filibrnnchia, 



1. Pecten medius, Lamarck, 1819. Plate 56, figs. 7, a. 



Pecten medius, Lamarck, A.s.V., vi, 1819, 163 ; Thes. Conch., i, pi. l.~>. 

 f. 102-4 ; Conch. Icon., viii, pi. 11, f. 44 ; Hartley, Cat. Rec. Biv. Shell-. 

 269 ; Medley, Mem. A.M., iv, pt. 5, 303 ; Pritch'ard and Gatlifl', P.R.S. 

 Vic., xvii (n.s.), 261. P. laticostatus, Gray, Tate N.Z., 1835, 310. Volx 

 laticoslatus, Gray, M.N.Z.M., 171 ; not of Lamarck, 1819. Pecten fuscus, 

 Sowerby, Thes. Conch., i, 47, pi. 16, f. 118, 119. P. fuinntus, Reeve, 

 Conch. Icon., viii, 1852, pi. 7, f. 32. P. (Janira) fumafus, Reeve, 

 (/hall. Rep., xiii, 307. P. fuwatus albus, Tate, P.R.S. Tas., 1887, 

 113. P. novce-zelandice, Reeve, i.e., pi. 8, f. 36. P. filosus, Reeve, 

 i.e., pi. 11, f. 42. P. nteridioiinlis, Tate, P.R.S. Tas., 1887, 114. 

 P. 'medius, Lamarck : Dall and Simpson, Moll. Porto Rico, 1901, 465 ; 

 Index, 93. 



Shell nearly orbicular, rather solid, with subequal ears, prominently 

 radially ribbed, attaining a large size. Beak of left (flat) valve minute, 

 that of the right (convex) valve median, incurved, convex. Ears large, 

 triangular, the anterior slightly larger. Dorsal margins short, straight, 

 sloping gently toward the anterior and posterior rounded margins. 

 Sculpture : Ears with faint radial ribs above and numerous incremental 

 lines and ridges ; right valve with wide rounded or flattened ribs, 

 numbering usually 16, which are sometimes broken up into smaller 

 ridges, crossed by very fine growth-lines ; left valve with strong radial 

 shoulders and narrow well-developed rounded ribs, the interstices 

 much broader than the ribs, with very dense somewhat lamellar 

 growth-lines ; the reversed radial sculpture well pronounced on the 

 inner side of the valves, the ribs being somewhat double near the 

 margins. Colour of right valve, purplish or whitish, sometimes faintly 

 marbled or with concentric rows of brown spots ; left valve red or 

 purplish, sometimes variegated with small lighter blotches, generally 

 having a lighter well-marked area at the beak. Interior white ; 

 sometimes the ears and the margins chestnut - brown. Margins 

 thin, sharp, undulating, that of the right valve extending beyond 

 the margin of the left valve. Hinge with 1 or 2 oblique lamella' 

 radiating from the apex (cardinal crura), and a faint lamella at the 

 base of the auricles (auricular crura), usually ending in a tubercle. 

 Resilium fairly strong, fixed in triangular pits underneath the 

 beaks. Adductor-scar large, round, somewhat posterior. Pallial line 

 simple. 



Diameter Ant.-post., 110mm. ; dorso-ventral, 92mm. : thickness, 

 30mm. 



Type in the Mus. Hist. Nat., Geneva. 



Hal}. North and South Islands of New Zealand, but more common 

 in the North. Chatham Islands. Also Tasmania, Australia, and West 

 Indies. 



This free-swimming shell is found on sand-banks at and below 

 low-water mark. 



Fossil in the Pliocene. 



