rn:i;ni \ 



1 . -i.nfess that I have Been n<> explanation <>f these facto which appears to me 

 < >ur knowledge of the direction in postages of ocean currents which must 

 have largely ilctcrmincd the distribution of pelagic forms in alight, and our record of 

 t'o->il 1'tiTojMMls is very imperfect. As far as I can ascertain, none are recorded from 

 S, ,uth America or South Africa, Imt it hardly seems possible to argue profitably about 

 the distriluation of the group in the past without definite information on this point 



Meanwhile it is interesting to observe that one Antarctic form, Clw ntloata, is 

 < !<>-< lv allied to a cosmopolitan form, < '/. pyramidata, and may plausibly be considered 

 M a -[,. . ;.il a.i iptatioii "t i! t.. Antai. 1 1.- lit'.-. AI-". i! wM0MM let ' ' i i~ a. hint i. ,| to 

 be merely a variety of L. rrf/wvmi, then L. retruversti is cosmopolitan and bipolar. Is 

 it not probable then that Clwne aiitarctica and Clione linuiciiui, plus some tropical 

 forms of the genus, represent variations of a once cosmopolitan species? There 

 is nothing unnatural in the idea that such a species may have undergone similar but 

 not identical changes in North and South Polar waters. The species of C'l /// 

 inhabiting the warmer seas ( CY. lontjiaiwlntu, Cl. flavtscens, and Cl. jmnctata) have not 

 been described in great detail, but they do not seem to differ from the Arctic and 

 Antarctic species so profoundly as to forbid the supposition that all may be modifica- 

 tions of one form. It is noticeable that the Arctic and Antarctic species have 

 invariably three pairs of buccal cones, whereas the warm water species have two pairs 

 or only one. The forms of Limacina which predominate in the tropics are not nearly 

 allied to L. antarctica and /,. helicina, but Dr. Meisenheimer states that /.. ranai 

 " weist ausserordeutlich nahe Beziehungen zu L. helicina auf," * although he separates 

 the two. This species, as to whose independence authors are not agreed, has been 

 found as far north as Lat. 33 S. L. helicuide*, which is known only by the shell, 

 resembles L. helicina and L. antarctica in having a Hat spire, though it is specific-ally 

 distinguishable. It is widely, though sparsely, distributed in the warmer waters of the 

 Atlantic, 



The anatomy of the Pteropods has been so fully described by various authors that 

 in the following notes I have not touched on it, except when necessary for purposes of 

 classification. My best thanks are due to Mr. T. J. Evans, Lecturer on Zoology in the 

 University of Sheffield, for preparing sections and drawings, and for much assistance. 







LIMACINA. 



Ten or eleven species have been referred to this genus, but the animals of 

 /.. rinctintfui and L. helieoides are unknown, and opinions differ as to whether all 

 the other species are really valid. The relationships of L. hclicina and L. nuinrctica, 

 as well as of L. retroversa, L. le&ueuri and L. awtrali* are discussed below. 



There is some difference of statement as to the presence or absence in tins 

 genus of organs called jaws, and possibly some variation in the texture of the 



SUdpoUr Expedition. Itcropoden, p. 106. 1006. 



