OCR Text |
Show 1904.] FROM EAST AFRICA AND ZANZIBAR. 99 in size. There are only very faint traces of a second row. The radula consists of 37 rows, with a maximum formula of about 90 + 1.1.1+ 90. The teeth are of the shape usual in the genus. The central tooth is finely striated, moderately wide and tricuspid, the central cusp being pointed, those at the sides blunt. From the buccal mass issues a long broad tube (4-5 mm. wide), which passes above and to the left of the genital organs, and then enters the liver, where it dilates into a stomach bearing a girdle of plates. These are about 120 in number, horny, fairly strong, brown, triangular, and of various sizes, the largest being 4 mm. long and T5 high, the smallest only a quarter of the size and white. The liver is large, yellowish externally, blackish internally. In coloration this animal resembles M. chloanthes B., but can hardly be identified with that species on account of the differences in the velum, jaws, central tooth of the radula, and stomach-plates. I think it is very probably identical with Pease's Tritonia haivai-ensis from the Sandwich Islands, but his description is not sufficiently detailed to make identification certain, and the expressions " Veil strongly digitate," " Tentacles \i. e. rhinophores] retractile into . . . laciniated sheaths," hardly apply to the present specimen. M. virescens and M. albo-tuberculata are closely allied and possibly only varieties of one species; but the present specimens exhibit some differences in the velum, median tooth, and digestive organs, as well as in coloration. M a r io n ia , species. One small specimen, dredged in 10 fathoms off' Wasin. It was dead when found and of a uniform opaque white. The velum was hardly digitate, but presented six undulations. The foot was broad. The alcoholic specimen has become deep brown and is somewhat decomposed. It is 5 millimetres long, 2 broad, and 1'5 high. The back is tuberculate, with a slightly projecting margin, which bears on each side 6 small branchiae set at a considerable distance from one another. The rhinophore-pockets are raised and simple. The velum appears simply circular. No jaws could be discerned. The radula was extremely small, and on a superficial examination appeared to be uniseriate, but on careful investigation was found to have the formula 5 .1 .5 . The laterals are all alike, thin and hamate. They are folded oyer the central tooth, a narrow plate with slight indications of being tricuspid. The stomach contained about 80 yellow plates, all of much the same size. This is perhaps an immature form in which the jaws are membranous ; but, if so, it is remarkable that the stomach-plates are fully developed. The extreme narrowness of the radula is also remarkable. The characters as described above are sufficient to constitute a new genus, but I hesitate to do this on the evidence of one minute specimen. V |