84 



In the genus Lottia of Gray, (Patelloideo^ Quoy,) we have 

 a remarkable instance, where animals, differing widely in the 

 arrangement of their respiratory organs, have, so far as hitherto 

 observed, an entire similarity of shells. So much so, that M. 

 Quoy, who described the animal, says that it is absolutely im- 

 possible to distinguish the shell from that of Patella; and also, 

 that here is a marked exception to the general rule, that an ani- 

 mal having the respiratory apparatus non-symmetrical will have 

 a non-symmetrical shell. 



By a careful examination of several well established species, 

 and numerous individuals, of this genus. Dr. G. thinks he has de- 

 tected a character which will nullify both the above remarks, and 

 enable us, by the shell alone, to distinguish the two genera in the 

 majority of cases. 



If we examine the anterior portion of the shell, corresponding to 

 the left side of the animal, we shall find a faint groove or undulation 

 passing, in direct continuation of the lateral margin of the cervical 

 portion of the muscular impression, to the margin of the shell, thus 

 taking nearly the diagonal line of the shell from its apex. This is 

 quite decided in L. gigantea, Gray, L. icstudinaria, i., and in 

 our own L. testudinalis, Mull. But in other species it is detected 

 with difficulty, sometimes merely by the play of light as the shell 

 is turned horizontally around. Nothing of the kind, whether dis- 

 tinct or faint, will ever be found corresponding to it on the opposite 

 side ; nor is it found in any species of true Patella that Dr. G. has 

 yet examined. In some specimens, and probably in some species, 

 this groove may not be visible ; but wherever it is discovered, the 

 shell may safely be referred to the genus Lottia. 



To constitute this a perfectly satisfactory diagnostic mark, we 

 ought to be able to refer to some organ of the body as its cause, 

 as we can for the groove in Sij)honaria. But the branchial plume 

 is here on the opposite side ; and there is no organ, so far as Dr. 

 G. has learnt, which corresponds to this mark ; and while we 

 cannot yet account for it on anatomical grounds, yet its presence 

 is too constant to be regarded as merely accidental. 



Mr. J. E. Teschemacher exhibited three specimens of ferns, 

 from the Sandwich Islands, of the genus Depairia of Hooker, 

 and made the following observations. 



