REPORT ON THE MONAXONIDA. Ixv 



distinction between the two. Moreover, the sigmata, which occur in both subfamilies, 

 are such a common and wide sjaread type of microsclera that their presence cannot be 

 safely relied upon in estimating probable relationships. From their extreme simplicity 

 it appears quite possible that they may have originated independently in several groups.' 

 We distinguish three genera in this subfamily, and we have already pointed out the 

 interesting fact, that here, as in the Homorrhaphidae, there is a very strong tendency 

 towards the development of horny fibre, which asserts itself as soon as the necessary 

 surroundings (viz., moderately warm and shallow seas) are attained. 



The Tedaniinas, which we have placed next in the series, are also a very isolated 

 group. The spiculation is, so far as the megasclera are concerned, identical with that of 

 the genus Myxilla amongst the Desmacidonidse, even down to the relative positions of 

 the two forms of spicules in the sponge. A very wide distinction lies, however, in the 

 fact that the Tedaniinas have no chelas, but, in place thereof, simple rhaphides, which are 

 unliuown in the genus Myxilla. The differentiation of the megasclera into " main " 

 and "dermal" forms, differing fundamently from one another in shape, must be con- 

 sidered as an indication of a high degree of specialisation and alone quite sufficient to 

 necessitate the removal of the Tedaniinse from amongst the Renierinse, where they have 

 been placed by previous authors. It seems not unlikely that here, as in the Phlceo- 

 dictyinse, the only two described genera will have to be merged into one ; for the 

 distinguishing character {i.e., the spination of the styli in Trachytedania) can hardly 

 be considered of generic importance {cf. the similar spination of the styli in some 

 species of the genera lophon and Myxilla). 



The Desmaeellinse are not a very satisfactory subfamily, for as yet we know hardly 

 anything about them. There is only a single established genus, viz., Schmidt's 

 Desmacella, and they differ from the Gelliinse only in the replacement of the diactinal 

 megasclera by monaetinal forms ; it is very possible that these two subfamilies 

 should be united, though we have found it convenient for the present to keep them 

 distinct. 



We come now to the last subfamily of the Heterorrhaphidse, viz., the Hamacanthinge. 

 In this subfamily we meet with microsclera of a very remarkable and entirely unique form, 

 the diancistra. These spicules seem to be peculiarly constant in shape in the different 

 species. That they have some connection with the ordinary sigmata of other sponges is 

 very probable, but they are always distinguished from these by the presence of a sharp, 

 cutting inner edge with three notches, one in the centre of the shaft and one at each 

 angle where the shaft bends round to form the terminal hooks. The nearest approach 

 which we have found to this spicule in any other genus is the large sigma of Esperella 

 simonis (PI. XV. fig. 13), which differs, however, in the absence of the characters just 

 mentioned, though resembling the diancistra in its unusually large size and in the shape 



1 Cf. Ridley, Zool. Coll. H.M.S. "Alert," Brit. Mus., 1884, p. 371. 

 (ZOOL. CHALL. EXP. — PAET LIX. — 1887.) Nnii i 



