2 = SIR C. ELIOT. 
distinct species, and not as varieties of L. helicina and of Clione limacina; but I 
have entered as ZL. retroversa specimens which others might be disposed to call 
L. australis or L. lesueuri. 1 have given below my reasons for these identifications 
and distinctions, but I recognise the possibility of interpreting the facts differently 
and also the uncertainty of some of the facts. An examination of several 
collections shows that both the shells and soft parts of Pteropods are very 
susceptible to the influence of the fluid in which they are preserved, so that 
individuals belonging to the same species may become superficially dissimilar in 
shape and colour. To this must be added the differences arising from age and 
local variation. But, making the widest allowance for such influences, I am still 
of opinion that the two chief Antaretic forms (L. antaretica and Cl. antarctica) are 
distinct from the corresponding northern species. 
The distinction is most clearly marked in the genus Clione. Comparing the 
Antaretic specimens with typical specimens of Cl. limacina, one may even say that 
they are a well-marked species, unless indeed they are immature, as might be 
areued from their small size and other features. The differences between Limacina 
helicina and L. antarctica are less noticeable, and some may think that the term 
variety is sufficient to cover them. But they are internal as well as external, and 
it seems to me safer to regard the forms as_ specifically distinct, at least 
provisionally. On the other hand, all the Limacinas with elevated spires collected 
by the ‘ Discovery, though showing considerable variation, form in my opinion 
only one specific type, and if this is admitted, I do not see how that type can be 
distinguished from JL. retroversa. The only differences lie in the colour and 
striation of the shell. Even if natural, they are hardly of specific value, and they 
are very likely due in part to the action of the fluid in which the animals were 
kept. The alternative of recognising about four separate species is possible, but 
not only do the forms pass into one another by intermediate stages, but they 
appear to live together. It is noticeable that Z. retroversa was not found as far 
south as L. antarctica and Cl. antarctica, and does not extend much beyond 
Lat. 60° 8. This agrees with the distribution recorded by other expeditions. 
Whether we call the Antarctic forms varieties or species is, in reality, a comparatively 
unimportant question. That there are some differences of detail between them and the 
Arctic forms everyone will admit; that the two sets of forms are nearly related is 
equally clear. The interesting point is that in both the Arctic and Antarctic seas the 
predominant, and as we approach the Poles probably the only Pteropods are closely 
allied, or even identical species of Limacina and Clione. The characters which these 
Arctic and Antarctic forms present are compatible with any hypothesis which assumes 
that they are derived one from the other, or from a common ancestor. Further, the 
distribution of these forms is interrupted by a wide zone in which they do not occur. 
None of them are recorded from within thirty degrees either north or south of the 
Equator, 
