OF THE LEYDEN MUSEUM. 201 



Species 2. Pneumoderma peroni (Lamarck). 



Atlantic Ocean, date?, 6 sp., Boie. 



The specimens are only badly preserved, and none of 

 them has its acetabuliferous appendages stretched out. 

 These are short, compressed and broad organs, and bear 

 at the median side (lateral when retracted) about 80 (not 

 100, according to Boas and Pelseneer) small suckers, all 

 of about the same size. They are provided with very ex- 

 tensible peduncles as Pelseneer (1887, p. 29) remarked: 

 now a group of suckers at the dorsal margin of the appen- 

 dage, now at the ventral margin or elsewhere, are strongly 

 stretched out by means of long peduncles. This phenomenon 

 becomes even yet more pronounced by the fact that the 

 acetabuliferous appendage itself is composed of some longi- 

 tudinal muscular bands, which can move rather independently 

 of each other, and are often mutually in a very different 

 state of contraction. So the whole may assume a variable 

 shape, difficult to be described. 



Family II. Olionidae. 



Genus 1. Clione Pallas. 



Species 1. Clione limacina (Phipps). 



Groenland, date?, 5 sp., ? 



Arctic Ocean, date?, 2 sp., cabinet Brugmans. 



Remarks on distribution , inferred from the 

 foregoing notes. 



Vertical distribution. The Pteropoda are known to inhabit 

 generally surface-waters, yet they seem to show an optimal 

 horizon of 50 and more fathoms. Recently we have ob- 

 tained some important dates about this fact by the in- 

 vestigations of Meiseuheimer (p. 93), Pelseneer and G. H. 

 Fowler (pp. 151, 154 and 155), andSchiemenz(pp. 28 — 30). 

 The iuvestigations of Mr. Buitendijk indicate that 

 Notes from the Leyden IMusouixi, "Vol. XXIX. 



