32 THE VOYAGE OF H.M.S. CHALLENGER. 



Observation. — The appearance of this small Pneumonoclerma, when its fins are a 

 little contracted, is very peculiar, and resembles very much that of some Cephalopods, 

 as, for example, Cranchia scabra, Leach. 



I have dedicated this species to Souleyet, whose remarkable works will always remain 

 the basis of our knowledge of the Pteropoda. After the death of this courageous 

 worker, his exceedingly able works on the anatomy of the Mollusca were nearly forgotten 

 in France, especially among the zoologists of Paris, where, however, the comparative 

 anatomy of Molluscs is held in esteem, and it is English, German, and Danish zoologists 

 (Huxley, 1 Bronn, 2 and Boas 3 ), that have given to Souleyet the position to which in my 

 opinion he is entitled. And since in that group of Pteropoda that Souleyet studied so 

 much and contributed so much to make known there is not one species bearing his 

 name, I have thought that the best way of showing my respect for his memory, was to 

 give his name to that new species which has the most remarkable appearance. 



As remarked previously, the other specific names of Pneumonoclerma are synonyms 

 of other already known species, with the exception of two names of Quoy and Gaimard, 

 already referred to, " Pneumodermon pellucidum"* and " Pneumodermon ruber." 5 



Boas thinks 6 that the first may be a Clionopsis, because it possesses a foot like that in 

 this genus. But according to the figure of Quoy and Gaimard, it has a well-developed 

 lateral gill like that in Pneumonoderma ; and Clionopsis does not possess such a gill. 

 This is therefore a point which throws doubt upon the exactness of the drawing of the 

 above mentioned writers, and which will at present prevent any decision in regard to the 

 systematic position of this species. 



As to the " Pneumodermon ruber" of the same writers, it certainly includes different 

 forms. 



First, a species (loc. cit., pi. xxvii. figs. 19, 20) which also possesses a foot as in 

 Clionopsis and a lateral gill as in Pneumonoderma, and in regard to which one must 

 make the same remark as regarding " Pneumodermon pellucidum." 



Second, a species (loc. cit, pi. xxvii. figs. 21-24) which possesses a foot and gill as in 

 Pneumonoderma, but which is so badly described and figured that there is no character 

 to distinguish it from the other species of this genus, or sufficient to identify it with one 

 of these species. 



Nothing can therefore be decided, either in regard to "Pneumodermon ruber" or 

 " Pneumodermon pellucidum," untd the forms which Quoy and Gaimard described under 

 these names are again obtained. 



1 On the Morphology of the Cephalous Mollusca, Phil. Trans., 1853, p. 52. 



2 Die Klassen und Ordnungen des Thierreichs, Bd. iii. pp. 585, 873. 



3 Spolia atlantica, pp. 9, 10. 



4 Voyage de decouvertes de l'Astyolabe, Zoologie, t. ii. p. 390, pi. xxvii. fig. 25. 

 6 Better rubrum. Loc. cit., t. ii. p. 389, pi. xxvii. figs. 19-24. 



6 Spolia atlantica, p. 171. 



