232 Scientific Proceedings, Royal Dublin Society. 



into two narrow channels running side by side before entering the penis, 

 which has a large pouch. The sexual precocity of the Gymnosomata is well 

 known: thus, Pelseneer (1887, p. 49) alludes to Clione flavescens (Ggbr.) of 

 hardly 2 mm. in length, and still possessing ciliated rings, as being able to lay 

 eggs ; and Kwietniewski (1902, p. 17) states that the sexual elements are known 

 to develop with much precocity in other Pteropods besides the above species. 

 Among the present specimens the smallest example with penis evaginated 

 measures "75 mm. in length. A number of small specimens with no outer 

 genitalia, but taken in hauls with those exhibiting them, have either the 

 accessory glands or gonad so swollen below the ventral surface, towards the 

 right side, that it seems inevitable that a rupture of the skin must occur, as 

 the sexual elements seem to be developing at a much greater speed than the 

 rest of the little animal. 



Distribution. — Atlantic, on a voyage from Brazil (type) ; Mediterranean 

 (Kwietniewski) ; off Brazil, one specimen (Schiemenz). 



Pneumodermopsis Michaelsarsi, Bonnevie. 



S.E. 224— Midwater otter trawl at 700 fathoms. Two. 



S.E. 438— Tow-net at 100 fathoms. One. 



S.E. 803— Tow-net at 50 fathoms. One. 



S.E. 943— Tow-net at surface. One. 



S.E. 1845 — Midwater otter trawl at 0-4 fathoms. One. 



" Thor " 6. VI. '06. 48° 43' N., 15° 17' W, 300 in. w. One. 1 



All the above, measuring T30-11 mm. in total length have had the 

 radula investigated. The median tooth is without a central denticle. The 

 lateral teeth diminish in length outwardly, the smallest being usually about 

 two-thirds of the length of the innermost tooth. The hook-sacs contain 

 about thirty to fifty hooks, of very unequal size. The youngest specimen, 

 of 1-30 mm. in length, has only about twenty hooks in each sac, and but 

 fourteen rows of teeth in the radula, instead of twenty or twenty-two rows, 

 as in larger specimens. 



The jaw, in the present examples, is more like Boas's illustration (1886, 

 tab. 8, fig. 119) of the same in P. ciliata (Ggbr.) than Bonnevie's drawing 

 (1913, pi. vi, fig. 47). It equals the radula in width, and is about one-quarter 

 of its length. Bonnevie (op. cit., p. 66) was unable to loosen the acetabuli- 

 ferous appendages of the type in toto, and, therefore, could not describe them 

 further than by giving an illustration [op. cit., fig. 48) of four suckers on 



1 This specimen was collected by the staff of the " Thor " somewhat south of our area, 

 but is included here because of its interest. 



