180 ARCID/E. 



certainly not that of Linne. Pennant made the same 

 mistake. It has had many other names, including 

 Mijtilus Garnseice (Petiver), A. crinita (Pulteney), A. 

 Gaimardii and A. Quoyii (Payraudeau), A. striata 

 (Reeve), and A. Pennantiana (Leach). 



I found a small single valve of A. nodulosa, Miiller, 

 in some dredged sand from Shetland. This species in- 

 habits the Swedish and Norwegian coasts, and occurs 

 at depths varying from 15 to 150 fathoms. The shell 

 is broader or more produced at each end, and thinner 

 than that of A. lactea ; the sculpture consists of several 

 longitudinal rows of vaulted or imbricated scales instead 

 of cross ribs ; and the teeth are not half so many as in 

 the other species, and they are placed more obliquely or 

 diagonally. It is closely allied to A. imbricata, but in 

 that species the inside margin is notched. A, aspera, 

 Philippi, from the Sicilian tertiaries, appears to be the 

 same as Midler's species. 



4. A. tetrago'na*, Poli. 



A. tetragona, Poli, Test. Sic. ii. p. 137, t.25. f. 12, 13; F.&H. ii. p. 2o4, 

 pi. xlv. f. 9, 10, and (animal) pi. P. f. 1. 



Body white : mantle having its border plain, but the upper 

 half of it on the posterior side is fringed with about 40 close- 

 set and equidistant ocelli or dark dots, which vanish or are in- 

 distinct towards the anterior side ; the margin is also mottled, 

 both above and below, with flakes of pale yellow : yills nearly 

 coequal in size, and striated, of a brown colour : lips ex- 

 panded, formed out of the extremities of the gills : foot white 

 and subcorneal, tapering to a blunt point, and furnished with 

 a deep byssal groove : byssus dark-green, composed of a few 

 leaf -like plates. 



Shell forming an irregular parallelopipedon, and angular, 

 sometimes twisted on the posterior side, very tumid, solid, of 

 a dull hue : sculpture, the same as in the last species : colour 



* Quadrangular. 



