| OCR Text |
Show racters of the genital organs, but, owing to the condition of the specimen, it is obviously far from being satisfactory, and in order to deal fully with this interesting species more material is. necessary. P rosthiostomum p a l l id u m , sp. 11. One specimen, from the sea-shore, Dec. 1899. Total length, about ........... 20 111m. Breadth, about................... 4 ,, Anterior margin rounded. Arrangement of eye-spots shown in text-fig. 56. 1 Text-fig. 56. 1 9 0 3 . ] POLYCLADS OF THE 44 SKEAT EXPEDITION." 31 7 e, marginal; br.e, brain eye-spots. Closely allied to P. siphunculus of the Mediterranean by the arrangement of the eye-spots, and agreeing with it apparently in being, so far as the spirit-specimen shows, of an uninterrupted dull grey-brown colour, it differs sufficiently in that the two rows of brain-eyes diverge continuously from one another from before backwards, whilst in the Mediterranean species these two rows converge at their middle. It is also readily distinguishable, I think, from the latter species by its smaller size. The single specimen obtained by Mr. Evans is, to judge from the state of the sexual apparatus, fully mature. P. siphunculus, moreover, has the genital sexual organs relatively much smaller, to judge from Lang's figures (see Lang, 4 Poly-cladida,' pi. 5. fig. 3). P. pallidum is certainly very distinct from any species from the Indian Ocean that I have had the opportunity of studying, and also, I believe, from the species found in the Pacific. I believe that Leptoplana aurantiaca of Collingwood is really a Prosthiostomum. It has the shape and proportions of a member of that genus, whilst its eye-spots have the characteristic Prosthiostomum arrangement. It may, of course, be identical with the |
