ADDENDA. 257 



The two others have an auricular projection as in the two last, but 

 the inner margin on the inside is furnished with a rib only and not 

 a detached margin, and the outer edge is not reflected: these are 

 the T. navalis, and the T. nana ; the former of which has the ac- 

 cessorial appendages elongated and spoon-shaped, as is represented 

 in our plate 2, fig. 3 ; the latter is distinguished by the strong pro- 

 jecting conic tooth on the cardinal margin, but the accessorial 

 appendages we have not as yet detected. 



Mytilus praecisus, p. 24. 

 We have specimens of this shell taken from the interior of 

 stone dredged in Torbay. It is a species of Saxicava, much allied 

 to the S. rugosa, but is flatter and thinner, with the valves more 

 unequal. 



Mya ovalis, p. 33. 

 We observed a specimen of this species in the cabinet of Mrs. 

 Grifiiths, taken among the rocks in Torbay. 



Sphenia Binghami, p. 37. 

 Minute and delicate specimens are found not unfrequently among 

 the fine sand sent us by Mr. Lyons, from Tenby. 



Lister A compressa, p. 51. 

 It is probable that there may be two species of this genus, as, 

 among our specimens gathered from difi"erent habitats, we observe 

 some which have two distinct denticles in one valve and one in the 

 other, all of them strong and erect ; others have three additional 

 denticles in one valve, and two in the other, all oblique and rib - 

 like. If so, the species with three oblique denticles in one valve 



