54 Memoirs of the Indian Museum. .[Voiv. V, 1915.] 



pores, seem to indicate that it lives more deeply buried than the typical form. Its 

 superficial resemblance to Sphenopus marsupium, an Actinian that lives buried in 

 mud and is common off the mouths of the Ganges, is noteworthy and affords an inter- 

 esting instance of convergence. Dendy l has pointed out that T. dacty-oidea is 

 closely related to the species he described under the name T. limicola, except in the 

 important feature that in the latter " the sponge is very compact throughout, and 

 there are no wide tubes in it, the excurrent canals being very narrow and opening by 

 numerous minute apertures in the floor of a somewhat flask-shaped cloacae with 

 slit-like vents on the surface of the sponge. " He rightly regards this feature as an 

 adaptive one connected with the fact that the sponge lives in very fine soft mud in 

 Lake Tamblegam, a comparatively small lagoon on the coast of Ceylon that closely 

 resembles the Chilka Lake in many respects. So far as its compact structure and 

 the absence of broad channels go, the Chilka sponge is very like the Tamblegam one, 

 but the nature of its single exhalent aperture is totally different. Although it lives 

 in sand, the water above it is always full of fine silt held in suspension. The case 

 seems to be in some respects parallel to one I have recently discussed elsewhere, viz. 

 that of Corvospongilla barroisi and Nudospongilla aster in the Lake of Tiberias.' 2 

 In both cases. we find sponges structurally related and living in the same, or a very 

 similar, environment, but adopting diametrically opposite means of protecting their 

 water-system; in both cases the disadvantages of their environment are due to 

 minutely separated mineral matter held in suspension in the water or settling on the 

 surface of the sponge. 



1 " Report on the Sponges " in Herdman's Ceylon Pearl Oyster Fisheries III, p. 94 (1905). 



2 Joitm. Âsiat. Soc. Bengal (n. s.) IX, p. 76 (1913). 



