1 16 MYTILUS. MUSSEL. 
one end : length two inches and a half; breadth five or 
six. 
In deep rivers and ponds, v. v. 
] S. Mytilus anatinus. .Duck Mussel. 
Lister, pi. 153. f. 8 — Pennant , pi. 71—Da Costa , pi. 15. 
f. 2— Donovan, pi. 113— Linn. Trans, viii. pi. 3 A. f. 2- 
Dorset Cat. pi. 12. f. 2, and pi. 13. f. 6. 
Shell oval, thin, deep green or blackish; the cartilage 
margin running straight, and then sloping suddenly and 
obliquely, forming a pointed angle about half way do^ ; 
inside perlaccous : beaks more or less decorticated, and the 
front margin terminating in a membranaceous skin ; length I 
two inches ; breadth hardly three. 
It differs from the last, in size, in the projecting angleon 
one side, and in the beaks, which are more or less decor, 
ticated. 
Variety. Thicker, more ponderous and rough, more aa- 
gular on the cartilage side, and a little contracted in front. 
Linn. 'Trans, viii. pi. 3 A. f. 3. 
It is evident that Maton and Rackett have misunderstood 
these two species, by inverting the references to their own 
plates. Da Costa properly observes that this last species 
differs “ in being only about half the size, rather more coin. \ 
pressed and oblong, and that the cartilage or lengthened i 
side extends or runs in a straight line to an acute angle, 
like a fin, and thence continues down the side in an ob¬ 
lique line, till near the bottom, where it is rounded.” 
Pennant and Dillwyn, in copying from them, have fallen 
into the same error. 
In ponds and deep rivers, v. v. 
19. Mytilus Avonensis. Avon Mussel. 
Linn. Trans, viii. pi. 3 A. f. 4— Lister, pi. 154. f. 9? 
Shell somewhat oval, thin, olive-brown, with transverse 
wrinkles. Resembles the last, but is broaderin proportion 
to its length, not so much produced at the hinge, the car¬ 
tilage side more rounded and less angular, and the front | 
margin runs nearly straight or is very slightly arched,par- I 
ticularly towards the smaller end. 
In the Avon, Wiltshire : rare. v. m. 
NAUTILUS. 
