116 MYTILUS. MUSSEL. 



one end : length two inches and a half 3 breadth five ov 

 six. 



In deep rivers and ponds, v. v. 



18. 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 down j 

 inside perlaceous : beaks more or less decorticated, and the 

 front margin terminating in a membranaceous skin : length 

 two inches ; breadth hardly three. 



It differs from the last, in size, in the projecting angle on 

 one side, and in the beaks, which are more or less decor- 

 ticated. 



Variety. Thicker, more ponderous and rough, more an- 

 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 com- 

 pressed and oblong, ajid that the cartilage or lengthened 

 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 Dillvvyn, in copying from them, have fallen 

 into the same error. 



In ponds and deep rivers, v. v. 



1.9. 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 broader in 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, pair 

 ^icularly towards the smaller end, 



In the Avon, Wiltshire : rare. v. m. 



NAUTILUS. 



