ON TTJRBELLARIA OF THE SCOTTISH NATIONAL ANTARCTIC EXPEDITION. 823 



scattered species of Turbellaria, are to be looked upon as new formations without 

 phylogenetic importance. 



It may be well to summarise here the points in which this new species of Aceros 

 differs from those previously described. 



A. stylo stomoides differs from A. inconspicuus, Lang (recorded from the Gulf of 

 Naples) : — 



1. By the number of eyes (a) in the brain groups (about fifteen in the former and 

 three in the latter on either side), and (6) in the tentacular groups (eight to nine in the 

 former and four in the latter on either side) ; 



2. By the presence in the former of a dorsal pore leading into the main gut ; 



3. By the absence from the former of special uterine glands. 



A. inconspicuus differs from A. nationalis, Plehn (recorded from the neighbourhood 

 of Cape St Vincent) : — 



1. By the much greater approximation in the former of the mouth and the male 

 aperture. In the latter these openings are separated by fully a sixth of the 

 body length ; 



2. By the number of eyes in the tentacular groups (eight to nine in the former and 

 thirty in the latter on either side) ; 



3. By the presence in the former of a dorsal pore and the absence of separate 

 uterine glands. 



POLYCLADA. 



Tribus Cotylea. Genus (nov.) Nuchenceros, referred provisionally to Fam. 

 Euryleptidce, Lang. Type, Nuchenceros orcadensis, n. sp. (Plate figs. 3-6). 



Two examples of this extremely interesting polyclad were obtained, the one 

 (specimen a) having its male structures in maturity, the other (specimen b) being 

 quite immature. They measure respectively 4*5 and 4 mm. in length, are oval in 

 shape, and of a brownish colour which is lighter underneath. The surface is destitute 

 of papillae. Their most striking characteristic is the presence of a pair of slender nuchal 

 tentacles studded with eyes and containing no visceral branches. The tentacles in 

 question measure an eighth of the body length, and are situated at a sixth of the body 

 length from the anterior margin. 



Eyes. — The eyes are in three groups on either side : (l) anterior marginal, three to 

 four in number, large, and embedded in the parenchyma ; (2) tentacular, about twenty-four 

 in number on either side, clustered thickly, especially on the outer and anterior sides of 

 the tentacles ; (3) cerebral, a somewhat diffuse group comprising (a) eyes right over the 

 brain, (b) eyes lateral to the brain, and (c) eyes behind the brain, and occurring as far 

 back as the junction of the first and second body thirds. The cerebral subgroups are 

 not definitely separated from one another, and the total number of eyes they contain 

 is about thirty on either side. 



