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Show 226 THE P0RIFERA OF THE THIRD TANGANYIKA EXPEDITION. [Mar. 6, EPHYDATIA PLUMOSA Carter var. BROUNI, nov. var. (Plate X"V II. figs. 11-13.) This new variety is represented by a small nodule 1*5 cm. in diameter growing round a twig, collected on the banks of the White Nile on land previously submerged, about 200 miles above Khartoum, by Mrs. Hilda Broun. The type specimens of the species were described by Carter, who found them growing on the sides of the freshwater tanks of Bombay, in which situation they were uncovered during six months of the year (Carter, Ann. Mag. N. H. 1849, (2) iv. p. 85). In 1885 Potts described (Proc. U.S. National Mus. 1885, p. 587) a variety of this species (var. palmeri) from the Colorado River, N.W. Mexico, differing from the type in having spined megascleres. The Colorado River specimens occur in thousands suspended like wasps' nests on the drooping branches of the Screw Bean, and exposed for ten months in the year. As Potts observes concerning the distribution : " That it should skip a whole hemisphere and only be found a second time at its own antipodes is indeed remarkable." Accordingly it is interesting to note an intermediate locality. The example from the Nile resembles the Bombay specimens in having smooth megascleres, but differs from the latter in the characters of the amphidisks and stellate microscleres. In the Nile specimen the stem of the amphidisks is markedly curved and considerably thinner at the centre than at the ends; in the specimens from Bombay and Colorado R. the stem is straight and uniform in diameter. The stellate microscleres in the Nile specimen are almost or entirely devoid of a centrum and the rays are not capitate, whereas in the type these spicules have a well-marked centrum and the rays are capitate. The characters of the spicules of the three forms are tabulated below:- Type specimen. JBombajr. var. palmeri. Colorado River. var. brouni. White Nile. Oxeas. 425 X 16 fi. Smooth. 325 X 12 fi. Spined. 392 X IGu. Smooth. Am}ihidisks. 1 Length 62/u. Diam. of disks 24 ft. Stem straight. Diam. of stem uniformly 4 ft. Length 78 /u. Diam. of disks 27 [*. Stem straight. Diam. of stem uniformly 6 fx. Length 63 \i. Diam. of disk 24 fi. Stem curved. Diam. of stem at centre 4^. Diam. of stem at ends 6 u. Stellate microscleres. With marked centrum ; " rays " capitate. With slight centrum ; rays not capitate; also other peculiar microscleres. Rays not capitate; without centrum. |