Synopsis Kkrisii-WATCR Mollusca 39 



Class LAMELLIBRANCHIA. 

 Order EULAMELLIBRANCHIA. 



Suborder SUBMYTILACEA. 

 Key to the families of Subuiytilacca. 

 ' ij'frament external 2. 



I T.igament internal 5- 



f Hinge with cardinal, anterior and posterior lateral teeth 4. 



2. \ Hinge with cardinal teeth only CyrcncUidcr. 



[ Hinge with lateral teeth only (no true cardinals) or edentate 3. 



f Gills with distinct, interlamellar septa, parallel with the gill 



3. \ filaments Un'wnidcc. 



I Gills either without distinct, interlamellar septa or, when 



[ present, oblique to the gill-filaments Margarilaiiidcr. 



{ Pallial line simple SpJicrriidcr. 



[ Pallial line sinuate Cvrenidce. 



( Hinge with cardinal and lateral teeth RangudcE. 



\ Hinge without distinct teeth Drcisscnsiidcr. 



Family MARGARITANID^. 



"Diaphragm incomplete, formed by the gills ; posteriorly the outer lam- 

 ina of the outer gills not connected with the mantle for a considerable dis- 

 tance ; anterior end of the inner gills separated from the palpi by a gap ; 

 branchial and anal openings ill-defined, and the latter not closed above; 

 no super-anal developed ; gills \^'ithout water-tubes and with scattered inter- 

 lamellar connections, which in certain places form irregular rows or with 

 continuous septa Avhich run obliquely forwards ; marsupium formed by all 

 four gills ; larva a small semicircular glochidium, without distinct hooks ; 

 shell elongated; sculpture of the beak concentric; hinge-teeth imperfect; 

 epidermis blackish." (Ortmann.) 



Genus MARGARITANA Schumacher, 1817. 



Shell elongated, usually arcuate, rounded in front, almost lacking a pos- 

 terior ridge ; beaks rather low, sculpture consisting of a few coarse, par- 

 allel ridges which follow the growth lines ; epidermis concentrically Striate, 

 brownish or blackish ; hinge-teeth generally imperfect or not fully devel- 

 oped, two more or less perfect pseudocardinals in the left valve and one in 

 the right, often reduced to mere tubercles ; laterals short, usually imperfect 

 or whollv Avanting: cavitv of the beaks rather shallow. 



