230 Scientific Proceedings, Royal Dublin Society. 



These twenty-nine records comprise over seven hundred specimens 

 measuring •40-4"50 mm. in length ; about half of them average 1 mm. in 

 length, and only a very small number measure more than 2 mm. Professor 

 D'Arcy Thompson took a small specimen (not preserved) outside Roundstone 

 Bay, Connemara, which he referred (Nichols, 1900, under Dexiobranchaea 

 pavxidens. Boas) to this species. In a previous paper (1909, p. 41) I suggested 

 that this record probably referred to P. ciliata (Ggbr.), of which species we 

 had met with a number of examples. At that time the larvae recorded above 

 had not been captured in some instances, and in others their small size caused 

 them to be put aside until a sufficient number bad accumulated for investi- 

 gation. Our present records appear to show that P. pauculens is by far the most 

 abundant of the two species off the coast of Ireland. Most of the hauls 

 were made off the west coast, from Cleggan Head, Co. G-alway, to the Fastnet 

 Light, Co. Cork, over soundings of 23-470 fathoms. It occurred also in five 

 hauls in St. George's Channel off the coasts of counties "Waterford and 

 Wexford, over soundings of 37-61 fathoms. Kwietniewski (1902, pp. 12-13) 

 found this species to be much more numerous in the Mediterranean than 

 P. ciliata. His largest specimen from amongst about thirty measured 4 mm. 

 in length, and the largest described by Boas measured 5 mm. He observes 

 that the larvae of the two species are difficult to distinguish exteriorly, but 

 that P. paucidens is a little more pigmented. About one-sixth of the present 

 specimens, measuring ■SO-S'SO mm., are devoid of pigment ; the remaining 

 examples, measuring from "40-4o0 mm., are usually thickly spotted with 

 small dark chromatophores all over the body except the fins. The pigment, 

 in some cases, is dispersed in clouds of pale purple-grey instead of spots. 

 Whether coloured or unpigmented, the radula, jaw, and hooks proved to 

 be identical in both these forms. In about sixty examples, including 

 individuals from all the hauls, the radula has been examined. In the case 

 of many others the suckers happened to be evaginated, so that no uncertainty 

 could be felt as to their identification. As described by Boas, a large median 

 sucker, with a smaller one on either side, followed by a lower pair, all 

 attached by long stalks to the median stem, are always present ; about ten 

 or twelve much smaller suckers on short stalks are placed on a transparent 

 membrane partially surrounding the median arm. The four lateral stalked 

 suckers are larger in proportion to the median one than in Boas' illustration 

 (1886, fig. 3, p. 158). The radula in the specimens examined was always 

 2-1-2, and the median tooth was without a central denticle; the inner 

 laterals had square, and the outer narrow, bases. A specimen of - 50 mm. has 

 twelve rows, and one of 4 - 50 mm. has twenty-two rows in the radula ; a 

 specimen of - 75 mm. has eighteen rows, and another of this length, and also 



