I?8 DISCOVERY REPORTS 



curved down as in Tesch's figure or in either of Pruvot-Fol's, and— as Tesch also claimed— the 

 denticles are lacking from the spine of the intermediate plate. The rest of the antero-median margin 

 is exactly as in Pruvot-Fol's first figure, and the three falciform laterals agree well with the previous 



illustrations. 



Differences "between this radula and that of Thliptodon rotundatus lie in the absence of the long 

 curlew's bill spine at the inner end of the intermediate tooth, and the smaller width of the median. 

 From both schmidti and gegenbauri, on the other hand, diaphanus is well distinguished by the greater 

 width of the median tooth compared with that of the intermediate tooth. 



MED. 



LAT. 



Fig. 4. Thliptodon diaphanus. (a) The radula, showing the median plate and the intermediate and lateral plates of one side. 

 INT., intermediate plate; LAT., lateral plate; MED., median plate, (b) Enlarged detail of the mesial edge of the intermediate 

 plate, (c) A bundle of hooks from the hook-sac of one side. 



Pneumodermopsis paucidens Boas 



1886 Pneumodermopsis paucidens Boas, Spolia Atlantica. Dansk. Vid. Selsk. Skrift. iv, 160, pi. vii, figs. 105-6. 



1887 Dexiobranchaea paucidens Pelseneer, 'Challenger' Reports, xix. Pteropoda, 1, 17. 



1926 Pneumodermopsis paucidens Pruvot-Fol, Moll. Pterop. gymnos. Res. Camp. Sri. Monaco, lxx, 12, pi. i, figs. 36-7. 



This species was very local in its occurrence in first survey material. It was taken in considerable 

 numbers at 50-100 m. and at 100-250 m. at WS 996, and makes a second appearance at WS 997, where 

 it was rather sparsely represented. It turned up nowhere else. Its greatest abundance at WS 996 may 

 be related to the heavy concentration of Limacina bulimoides, since it is chiefly upon small thecosomes 

 that these Gymnosomata are thought to feed. A close agreement is apparent between the depth 

 distribution of P. paucidens at station WS 996 (Fig. 5) and that of Limacina at the same station. The 

 night station, WS 997, did not yield sufficient numbers of individuals for an adequate comparison, but 

 the day-time distribution of this gymnosome is in agreement with Meisenheimer's conclusion (1905, 

 p. 98) that the Gymnosomata (' Tagtiere ')— unlike most of the thecosomes— approach the surface 

 by day. 



