Massy — The Gymnosomaious Pteropoda of the Coasts of Ireland. 227 



Family PNETJMODEBMATLDAE. 



Pneumodermopsis ciliata (Gegenbaur). 



Dexiobranchaea ciliata, Boas. 



S.B. 443 — Midwater otter trawl at 550 fathoms. Two. 



S.B. 449 — Midwater otter trawl at ca. 700 fathoms. Fourteen. 



S.B. 751— Tow-net at 50 fathoms. Three. 



S.B. 752 — Midwater otter trawl at surface. Three. Tow-net at surface. 



One. 

 S.B. 1385— Tow-net at 50 fathoms. Two. 

 S.B. 1386— Tow-net at 50 fathoms. Three. 

 S.B. 1387— Tow-net at 50 fathoms. Two. 



The thirty specimens recorded above measure T50-15 mm. in length. 

 The examples from station S.B. 751, measuring T50-2 mm. in total length, 

 have an unpigmented body with ciliated rings, a long posterior lobe to foot, 

 and the commencement of a lateral gill ; about eighteen rows compose the 

 radula of 5-1-5 or 6-1-6 ; the median tooth is without a central denticle, and 

 its base is not so prolonged as in Boas' figure (1886, tab. 8, fig. 11 6). The speci- 

 mens can be readily distinguished from similar-sized larvae of P. paucidens 

 (Boas), as each hook-sac displays about thirty hooks instead of six, and also 

 by the presence of the two very large suckers with a spine. The sucker 

 on the summit of the median arm is developed, and there are six or seven 

 suckers on each of the lateral arms. These specimens show a great advance 

 in development when compared with a larva of P. ciliata of 1 mm. in length, 

 described by Kwietniewski (1902, p. 11), in which the gill was still absent, the 

 radula only 3-1-3, and but five or six spines were present in the hook-sacs ; 

 the acetabuliferous appendages in this larva were still rudimentary, each 

 lateral arm possessing only two suckers, while the median arm only showed 

 the large left sucker, and a prominence where the large right one would 

 develop later, and there was no trace of a median sucker or of the lower 

 lateral pair. Schiemenz (1906, p. 25, tab. 1, fig. 10) was unable to discover 

 these latter suckers. In specimens in our hauls the lower pair of suckers is 

 certainly developed on the median arm, but they are so much smaller than 

 the suckers of the lateral arms, and on such delicate stalks of very variable 

 length, that they are by no means easy to see. The unpaired sucker of the 

 median arm is sometimes about twice the size of the suckers of the lateral 

 arms, and at other times it is equal in diameter to four lateral arm suckers. 

 The latter are usually equal in size, but in some specimens the proximal 

 suckers are the smallest, and they increase in size distally. Nine were 



