138 MOLLUSC A. 



flesh-coloured, more or less speckled with purplish ; the 

 under parts of the arms were bluish-grey ; the suckers whit- 

 ish." The specimens which furnished an opportunity for 

 making the preceding observations, were met with in the 

 Gulph of Guinea, and afterwards on the voyage, swimming 

 in a small argonauta, on the surface of the sea. The reader, 

 who is desirous of farther information on this subject, may 

 consult Dr. Leach's Observations on the Genus Ocythoe of 

 Rafinesque, Sir E. Home on the Distinguishing Characters 

 between the Ova of the Sepia, and those of the Vermes Tes- 

 tacea that live in water, in the Philosophical Transactions 

 for 1817, art. xxii. and xxiii., (both of which are added to 

 the appendix of Captain Tuckey's Narrative,) and a paper 

 by Mr. Say, on the genus Ocythoe, in the Phil. Trans. 

 1819? art. vii. More recently, however, naturalists seem 

 disposed to reunite the Ocythoe with the Argonauta, though 

 the question cannot be considered as determined. 



CLASS II. PTEROPODA. 



Fins formed of membranaceous expansions. 



This class was instituted by Cuvier, for the reception of 

 a few genera, the peculiar characters of which indicated the 

 impropriety of suffering them to remain in any of those 

 categories which had been previously established. All 

 the species are small in size ; and the attempts hitherto 

 made to investigate their internal structure, have, in a great 

 measure, failed in explaining the functions of the organs 

 which are exhibited. The valuable papers of Cuvier, on 

 the Clio, Pneumodermon and Hyalea, include nearly all the 

 accurate information on the subject, of which naturalist- 

 are in possession. 



