Massy — The Gymnosomatous Pteropoda of the Coasts of Ireland. 239 



not easy to discern them. About twelve rows are usually present in a radula. 

 The number of hooks (fig. 5d) projecting from the mouth of a sac varies from 

 thirty to fifty. In large specimens, the penis is evaginated behind the right 

 fin ; in small examples, it is visible beneath the visceral envelope above and 

 behind anus, the latter being placed on the right ventral side below the fin. A 

 long projection is present at either side of anal aperture. Dr. Meisenheimer 

 of Marburg, having made a superficial examination of some specimens pre- 

 viously recorded (Massy, 1909, pp. 49-50), thought that the example recorded 

 above from station S.E. 401 was T. Gegenbauri, Boas. The other examples 

 recorded at the same, time are no longer available for examination, but the 

 example from station S.E. 282, previously (op. tit., p. 50) identified by Dr. 

 Meisenheimer as T. diaphanus, must have been so named by him as a slip 

 for T. Gegenbauri, as the lobes of the foot are placed close together, instead 

 of being widely separated, as in T. diaphanus. An examination of the radula 

 proves it to be T. atlanticus. The young example from station S.E. 337, and one 

 of the specimens from station S.E. 270, have been previously recorded (op. cit., 

 p. 50) as Thliptodon sp. In the present list of seventeen specimens all have 

 had the radula examined, with the exception of four examples (three from 

 station S.E. 270, and one from station S.E. 590), in which it is missing from 

 mutilation ; but in all other respects these specimens agree with their 

 companions from these hauls. 



Thliptodon rotundatus, sp. n. 



(Plate VIII, fig. 6.) 



S.E. 443— Midwater otter-trawl, at 550 fathoms. Three. 



S.E. 449 — Midwater otter-trawl, at 700 fathoms. One. 



S.E. 481 — Midwater otter-trawl, fishing at ca. 600-900 fathoms. One. 



These have a round body, the posterior portion below the fins being nearly 

 equal in bulk to the anterior region (PI. viii, fig. 6a). Length, 3-4 mm. by 

 2-50-3 mm. in breadth. A ciliated band is present posteriorly. Viscera 

 extending nearly to end of body. Foot : three lobes (the posterior short and 

 pointed), placed close together just above fins. The latter are not so narrow 

 at base, or so wide distally, as in the last-named species. Sucking-disk 

 present. The skin pockets, containing the foot and fins, seem to be deeper 

 than in T. atlanticus, and the skin is much wrinkled elsewhere. Eadula: 

 3-1-1-1-3. Lateral teeth (fig. 6c) of the type peculiar to the family. Inner 

 lateral tooth with a rounded prominence towards the centre of outer edge 

 and no spur at the free end. Median tooth (fig. 6b; crescent-shaped and 



SCIENT. PKOC. R.D.S., VOL. XV., NO. XXII. 2 Q 



