Tertiary.-] PAL-ffiONTOLOGY OF VICTORIA. IMollusca. 



Plate XXXIV. 

 PECTEN YAHLENSIS (Wood). Var. SEMI-L^VIS (McCoy). 



[Genus PECTEN (Bkdg.). (Sub-kingd. Mollusca. Class Laraellibranchiata. Order Pleu- 

 roconcha. Fara. Pectinida».) 



Gen. Char. — Shell depressed, upper valve most convex ; slightly inequilateral ; beaks con- 

 tiguous ; hinge line produced into ears on each side of the beak, the anterior largest and 

 separated from the body of the shell in the lower valve by a deep notch for the passage of the 

 byssus ; ligament external, forming a narrow line along the hinge margin ; cartilage internal in 

 a triangular pit beneath the beaks ; with, or without, radiating hinge-teeth.] 



Description. — Sub-orbicular, apical angle 145°, ears nearly equal sub-quadrate, 

 sharply defined, anterior ear of right valve notched for passage of bj'ssus of attach- 

 ment. Right valve deeper than the left one, moderately and evenly convex, most so 

 near the middle ; beaks depressed ; surface smooth, with irregular lines of growth, 

 strongest on the posterior ear, above the dorsal margin of which they rise as pro- 

 jecting angular scales. Left valve nearly flat, slightly convex in the middle, and 

 slightly concave towards the sides ; ears with the posterior one a little longer than 

 the anterior one, but both slightly obtuse-angled ; surface radiated with very 

 numerous, sub-equal (or very rarely alternate) nearly straight, narrow, rounded 

 ridges, about one-tbird of their thickness apart, with an occasional slight irregular 

 flexuosity, crossed by sharp, erect, concentric, scaly larainte of growth, slightly farther 

 apart than the thickness of the ridges (about 8 or 9 ridges in middle of shell in space 

 of 3 lines at 2 inches from beak, about 5 in same space at 4 inches from beak) ; 6 

 to 9 narrow radiatins' rids'es on each ear, with transverse scales rather closer than 

 those of body. Length of large specimen, 4 inches 1 line (more commonly about 

 2 inches); proportional width from beak to opposite margin, -^^^ ; length of anterior 

 ear, -,%% ; of posterior ear, ^5% ; greatest depth (about middle) of right valve, -f^^ ; 

 of left valve, -j-iij' Substance of valves thin. 



Reference.— Rev. J. E. Woods, Ad. Phil. Soc. 1865, t. 1, fig. 4. 



The tj])ical variety differs form the above in having the right or 

 deeper valve radiated with from 59 to 67 strong, straight, moderately 

 convex, rounded, sub-equal ridges, separated by shallow concavities, 

 rather less than the width of the ridges (4 or 5 in 3 lines at 2 inches 

 from beak, 2 in same space at 4 inches from beak), and crossed by 

 lines of growth which are only conspicuous or interrupt the smooth- 

 ness of the radiation at wide irregular intervals, or near the lateral 

 edges of old specimens. In some specimens of this variety, too, the 

 ears are indistinctly radiated, and one gigantic specimen, presented 

 by Mr. Howitt from Bairnsdale, has a length of nearly 5 inches, 

 and the valves almost equally convex. 



Although color varies much in different individuals of many 

 species of Pecten, it is extremely unusual in this genus for the 



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