238 Scientific Proceedings, Royal Dublin Society. 



clearly in Bonnevie's fig. 53 (op. cit., p. 76), are of the type seen in his fig. c 

 (p. 75) for his Microdonta longicollis. In the largest specimen the radula is 

 composed of thirty rows of 6-1-6 ; the hooks in each sac number fourteen, 

 and the same number of spines appears in the jaw. A specimen 4 mm. in 

 length has twenty-one rows of 5-1-5 in the radula, fourteen hooks in each 

 sac, and twelve spines in the jaw. In addition to the clear cells behind each 

 hook-sac observed by Bonnevie, some of the present specimens exhibit a few 

 tear-shaped cells with a dark core extending in a single line on either side 

 of the jaw to the hook-sacs, each cell being about half the size of one of the 

 spines of the jaw. 



Distribution.—^ 26' K, 9° 20' W., surface ; 48° 29' N., 13° 55' W., 

 150 metres (Bonnevie, 1913). 



Family THLIPTODONTIDAE. 

 Thliptodon atlanticus, sp. n. 

 (Plate VIII, fig. 5.) 

 S.R. 270 — Midwater otter-trawl, at ca. 350 fathoms. Nine. 



S.B. 282 — Tow-net at 750 fathoms, over soundings of 1000 fathoms. One. 



S.R. 337— Midwater otter-trawl, at 400-450 fathoms. One. 



S.R. 401— Tow-net on trawl, 600 fathoms. One. 



S.R 481 — Midwater otter-trawl, fishing at ca. 600-900 fathoms. Two. 



S.R. 590 — Midwater otter-trawl, at 480 fathoms. Three. 



The specimens, measuring 3-7 mm. in length, resemble the form of 

 T. diaphanus, Meisenheimer (1905, pi. xvi, fig. 10), except that the portion of 

 body above fins, containing the enormous hook-sacs, radula, and gullet- 

 bladders, occupies about twice the bulk of the pointed posterior portion 

 (PI. viii, fig. 5a). Viscera not extending to end of body, which, in the best- 

 preserved specimens, shows a ciliated ring. Foot : a small three-lobed plate, 

 placed half-way between fins and top of head. Fins narow at base, widening 

 considerably distally. Sucking-disk present at centre of fins. Radula : 3-1- 

 1-1-3. Lateral teeth (fig. 5c) of the type figured by Boas (1886, pi. viii, fig. 122) 

 for his Thliptodon Gegenbauri. In the present species, the spur near the free 

 end of the inner lateral tooth is placed towards the centre of the distal 

 margin, instead of at the outer end. The median tooth (fig. 5b) consists of a 

 thickened undulating ridge, somewhat variable in form, but always with a 

 median projection and oblong, shovel-like ends, directed outwards instead of 

 inwards, as in Meisenheimer's (1905, pi. xxvii, fig. 3 m.z.) figure of T. diaplianns. 

 There are also anterior and posterior lines, but these are so delicate that it is 



