226 THE PORIFERA OF TK3i THIRD TANGANYIKA EXPEL>rnON. [Mar. 6, 



Ephydatia plumosa Carter var. beouni, nov. var. (Plate XYII. 

 figs. 11-13.) 



This new variety is represented by a small nodule 1*5 cm. in 

 diameter growing I'ound a twig, collected on the banks of the 

 White Mle on land previously submei-ged, about 200 miles above 

 Khartoum, by Mi'S. 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 (yar. jxdmeri) from the Colorado 

 River, ISr.W. Mexico, diftering 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 i-emarkable." Accordingly it is 

 interesting to note an intermediate locality. 



The example from the Nile resembles the Bombay specimens 

 in having smooth megascleres, but difiers from the latter in the 

 characters of the amphidisks and stellate microsclei'es. 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 E. 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 : — 





O.veas. 



Ampliidislcs. 



Stellate microscleres. 



Type specimen. 

 Bombay. 



4.25 X 16 ji*. 

 Smooth. 



Length 62 fi. 



Diam. of disks 24 (i. 



Stem straight. 



Diam. of stem uniformly 4 p.. 



With marked 



centrum ; 



" rays " capitate. 



Yur. pa J meri. 

 Colorado River. 



325 X 12 11. 

 Spiued. 



Length 78 j". 



Diam. of disks 27/*. 



Stem straight. 



Diam. of stem miiformly 6ju. 



With slight centrum ; 

 rays not capitate ; 

 also other peculiar i 

 microscleres. 1 



var. hrouni. 

 White Nile. 



392 X 16 ;u. 

 Smooth. 



Length 63 fi. 



Diam. of disk 24/*. 



Stem curved. 



Diam. of stem at centre 4/*. 



Diam. of stem at ends 6 u. 



i 



1 



Rays not capitate ; | 



without centrum. 1 



