WINdKV/ORTH : BRITISH SPECIES OF ANOMIA. 33 



exaggerated into prickles. Gill, W-sh.aped, without the fifth lamella 

 of flap of ephi'p'pium (PI. I, f. 2). Further, in addition to the row of 

 ciliated discs at the lower angles of the lamelloe, which are found also 

 in Anomia, there are in Monia other intermediate rows of ciliated 

 discs along the faces of the filaments. In this species there is one of 

 these in the outer and two in the inner lair^ella. 



3. SQUAMA, Gmelin, 1791 = A. striata, Loven, non Bolten = 

 A. glauca, Monterosato. Gmelin's species is based on Chemnitz, 

 viii, 697, where the figure is recognizable and the description un- 

 mistakable, locality Drontheim. In this species the shell adductor 

 immediately adjoins the byssal muscle on the left side of the animal, 

 so that the two form one continuous scar on the upper valve (PL I, 

 f . 10) ; this part of the shell is a deep green. The gill is of the same 

 kind as that of the last species, but the filaments are typically very 

 much finer and the number of intermediate ciliary rows is two and 

 three, usually, instead of one and two, but may be more numerous 

 in part or throughout (PI. T, f. 3). Typical examples always show 

 on the upper valve the peculiar striated sculpture of numerous 

 crowded rows of minute radiating scales. 



One form of this species to which I give the name of var. crassa, 

 as I am unable to identify it with any of the numerous Anomiidoe 

 Avhich have been described, is so difierent that I at first thought it 

 a distinct species both from shell and animal characters. It is very 

 much thicker, particularly in the coarse upper valve : the surface 

 occasionally shows traces of the typical squama sculpture, but is 

 usually much encrusted and devoid of sculpture (PI. I, f. 13-18). It 

 is markedly convex from its habitat on the convex side of Pecten. 

 Muscular scar much as in type, but the shell adductor is com- 

 paratively more dorsal, forming an anterior prolongation of the 

 byssal scar (PL I, f. 11). Gill similar, but the separate filaments 

 larger and coarser, and the intermediate ciliary rows are highly 

 irregular, usually three and four or more (PL I, f . 4), while in typical 

 squama these rows are regular. The hinge process on the lower 

 valve is enormously developed, and the border of this valve has a 

 wide green margin within. But these and other differences do not 

 seem to me essential, and I have no doubt as to its being a variety 

 of squama, modified by its more exposed habitat. 



Genus HETEKANOMIA, nov. Type, A. squamula, L. = A. aculeata, 



Miiller. 



Anomiiform molkisca, in which the gill lamellae have descending 

 filaments only, each gill being therefore fl shaped in section. The 

 alimentary and circulatory systems show it to be allied to Anomia 

 and Monia. The lateral asymmetry is strongly marked, so that the 

 right gill is not much more than half the length of the other. 



4. SQUAMULA, L. 1758 = A. aculeata, Miiller. There is no doubt 

 that this is the Linnean species from the habitat on seaweed and 



VOL. XV. — APRIL, 1922. 3 



