152 Records of the Indian Museum. [Vol. X, 



The spicules do not agree precisely with those of any of 

 the forms included in the synonomy of M. aegagropila b}^ 

 Vosmaer and Pekelharing, who have discussed the species in an 

 exhaustive manner. I, therefore, describe my specimens as the 

 type of a new "variety." Whether it is a true variety or a 

 geographical race (subspecies) cannot of course be settled until 

 more is known of the smaller and more delicate sponges of Indian 

 seas. 



The authors mentioned in the preceding paragraph found 

 M. aegagropila only on young oysters [op. ciL, p. 29). They 

 describe the method of growth as follows : ' ' They [the sponges] 

 formed their crusts, generally not more than 0-5 or i mm. 

 thick. They often covered the shells entirely, growing over the 

 free borders. If new layers of shell are formed, the sponge 

 immediately covers them. Hence in sections there can be found 

 shell-layers in the middle of the sponge body." Nothing of the 

 kind occurred in the case of sponges growing on mussel-shells at 

 Madras, but these shells are of course much smoother than oyster- 

 shells and the layers of calcareous matter of which they consist 

 are much more closely compacted. No sponge that I saw grew 

 over the edge of a shell, although in some cases the exposed 

 surface of one valve was almost completely covered. 



Mycale mytilorum, sp. nov 

 (Plates X, fig. I and xi, figs. 2, 3.) 



The sponge forms a delicate film not more than 2 mm. thick 

 and of a bright brick-red colour ; it sometimes covers the whole of 

 a large mussel-shell. In spirit the colour, which is apparently 

 not due to the presence of symbiotic algae, disappears rapidl}^ 

 The external surface is smooth except for the presence of angular 

 and apparently (not actually) spiny ridges on the central parts, 

 often interrupted and never as much as i mm. high. These are 

 largely artifects, not being visible in the living sponge; they 

 occupy the spaces between the superficial exhalent canals. 



Both dermal pores and oscula are minute and inconspicuous. 

 The latter are situated in the central, thicker parts of the sponge; 

 their position is indicated by the course of the superficial canals 

 that converse towards them. The dermal pores, when not 

 entirely obliterated by contraction, are oval in outline and of 

 variable size ; they are scattered on the peripheral parts of the 

 sponge. Their position can be dicovered readily by the aid of 

 a hand-lens, because they open, either directly or by short 

 passages partly closed by diaphragms, into larger circular lacunae 

 belonging to the inhalent system. These extend downwards 

 nearly to the base of the sponge and the finer inhalent canals 

 lead from them to the ciliated chambers. The finer exhalent 

 canals open into broader ones which run obliqueh' upwards 

 through the sponge and, long before reaching the oscula, form 



