2 SIR C. ELIOT. 



distinct species, and not as varieties of L. helicina and of Clione limacina ; but I 

 have entered as L. retroversa specimens which others might be disposed to call 

 L. oust ralis or L. lesueuri. I 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 Antarctic forms (L. antarctica and CL antarctica} are 

 distinct from the corresponding northern species. 



The distinction is most clearly marked in the genus Clione. Comparing the 

 Antarctic 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 

 argued 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 L. 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 L. retroversa was not found as far 

 south as L. antarctica and Cl. antarctica, and does not extend much beyond 

 Lat. 60 S. 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. 



