Perten.] PELECYPODA. 881 



the right valve is ornamented with concentric lamellae of growth which 

 cross a few radiating ridges, and it is rather deeply cut in beneath. 

 The hinge-line occupies the whole length of the shell, and above the 

 centre the umbo of the left valve is slightly prominent. 



Length, 2mm.; height, 1-75 mm. ; diameter, 0-5 mm. (E. A. 

 Smith). 



Type in the British Museum. 



Hab. Foveaux Strait, one specimen (A. Hamilton). The type is 

 from Prince Edward Island, in 100 to 150 fathoms. 



8. Pecten transenna, n. sp. Plate 52, tig. 3. 



Left valve minute, somewhat oblique, roundly ovate, with straight 

 dorsum and subequal ears, translucent, white, very thin and fragile, 

 moderately convex, with numerous radial riblets and concentric- 

 threads. Beak slightly anterior, a little raised, rounded, and smooth. 

 Ears subequal, small, not distinctly marked off from the disc. Anterior 

 end a little shorter, convex, receding below, slightly sinuated below the 

 ear ; posterior end straight above and rapidly descending, produced 

 and convex below ; the ventral margin broadly convex. Sculpture 

 consisting of numerous fine radiate riblets, with a few secondary 

 shorter riblets, crossed by subequidistant fine concentric lines, the 

 points of intersection with small tubercles. Colour white. Interior 

 white, shining, smooth. Hinge-line straight, with a small triangulai 

 resilium beneath the umbo. 



Diameter Ant. -post., 34 mm. ; dorso- ventral, 3 mm. : thickness, 

 1 mm. 



Right valve not seen. 



Type in my collection. 



Hab. Near the Snares, in 50 fathoms (type) ; near the Bounty 

 Islands, in 50 fathoms (Captain Bollons). 



ORDER 3. EULAMELLIBRANCHIA. 



Pelecypoda in which the edges of the mantle are generally united 

 by one or two sutures. Two adductor muscles are usually present. 

 In the gills the branchial filaments are united at regular intervals by 

 vascular junctions, which transform the linear interfilamentar spaces 

 into a series of fenestrae. Similarly the lamella? of each gill-plate 

 have vascular junctions which form afferent vessels in the interior 

 of the plates. The gonads always have their own proper external 

 orifices. 



SUBORDER 1. OSTRACEA. 



Monomyarian Eulamellibranchia, or with a very small anterior 

 adductor muscle. The mantle is open, without siphons ; the foot 

 rather small or absent, generally no byssus ; the branchiae folded. 



