842 PELECYPODA. [Filibranchia. 



curved, and bears the fossette of the ligament ; this valve has only a 

 single adductor-muscle scar ; pallial line entire. 



Distribution. European seas, America, Antilles, India, Japan, 

 Australasia, &c., from the laminarian to the coralline zone. 



Fossil the genus appears in the Devonian ; a few species are known 

 from the Cretaceous and Tertiary. Two or three species occur in the 

 Tertiary of New Zealand. 



Vernacular Name. Saddle-oyster. 



Remarks. The animal of .4. ephippium, L., has been described by 

 S. P. Woodward in A.M.N.H. (2), xvi, 1855, 23. 



According to Dr. W. H. Dall, the relative positions of the adductor 

 and byssal scars on the left valve are not constant in the same indivi- 

 dual at all ages, and small differences of this kind cannot safely be 

 used as specific distinctions. The best character seems to be the more 

 minute surface sculpture when fully developed in normal specimens. 



KEY TO SPECIES. 



A. Surface of left valve with radiate ribs. 



a. Ribs narrow, nodulous, bifurcating. Upper byssus-scar long, 



tongue-shaped. Colour whitish-yellow. Shell small . . furcata. 



aa. Ribs irregular, interrupted. Upper byssus-scar rounded. 

 Left valve honey-yellow, right valve green. Shell attain- 

 ing a large size . . . . . . . . . . W alter i. 



B. Surface of left valve without radiate ribs. 



a. Imbricating concentric lamellae ; interior purplish in the centre Huttoni. 

 aa. Concentric stria 3 and broad subparallel mostly oblique grooves ; 



interior white . . . . . . . . . . undata. 



1. Anomia furcata, Suter, 1907. Plate 51, iigs. 6, 6'/. 



Anomia furcata, Suter, T.N.Z.I., xxxix, 1906 (1907), 262, pi. 9, f. 9, 10. 



Left valve circular to oval, sometimes irregular, convex, thin, 

 semitransparent, radiately costate, and with distinct concentric 

 ridges. Beak distinct, nearly smooth, and more or less median ; one 

 specimen has a deep posterior notch, another example has 3 deep 

 posterior notches, and 2 shallow ones on the anterior end. The dorsal 

 margin is either straightened or flatly convex. The sculpture consists 

 of narrow nodulous radial riblets, obsolete in some places, and mostly 

 bifurcating towards the margin. The concentric ornamentation is 

 formed by fine close and slightly undulating lines of growth, inter- 

 spersed with distant stronger ridges. Colour whitish-yellow. Interior 

 of the same colour, and somewhat pearly, with a sharp and smooth 

 margin. There is a well-marked transversely elongate ligamental 

 fosette. The upper byssus muscle-scar is long, tongue-shaped, the 

 lower small and oval ; and the valve adductor-scar is of about the same 

 size, and triangularly oval. Pallial line entire, simple. 



Dimensions of a left valve : Length, 16 mm. ; height, 1(5-5 mm. : 

 diameter, 3 mm. 



Type in the Dominion Museum, Wellington. 



Hob. Near Channel Island, Hauraki Gulf, in 25 fathoms. 



