254 



•ENDEAVOUR" SCIENTIFIC RESULTS. 



smoothness of its echinating spicules ; in its restricted sense, 

 it will be more correct to say of the genus that it differs from 

 Clathria in the absence of accessory spicules. 1 he genus is, 

 however, a very generalised one and such species as might be 

 included in it are capable of derivation from a number of 

 different genera. 



Owing to such species as Clathria transiens, Echinochalina 

 intermedia, Whitelegge, O. tenuis, Carter, O. tubulosa, sp. n., 

 and O. nidificata, Kirkpatrick,! the task of satisfactorily de- 

 fining Ophlitaspongia is rendered rather difficult. With the 

 exception of O. nidificata (for which almost unquestionably a 

 new genus should be established) the species of which I have 

 information seem to require some such definition as the follow- 

 ing : "External form various, but never regularly honey- 

 combed. Skeleton a reticulation of usually well-developed 

 horny fibre which is cored or echinated, or both cored and 

 echinated by smooth basicaU styli (sometimes accompanied by 

 oxeote modifications). The basical styli, which are typically 

 of a single kind, may exhibit some degree of differentiation 

 into two kinds, but there is never any definable difference of 

 form between those which core and those which echinate, the 

 fibres. Monactinal auxiliary spicules, occurringf Interstitially 

 and in the dermal layer, are typically present. Microscleres, if 

 present, are isochelae palmatae and (or) toxa." 



In O. papilla, Bowbk., the type-species, and in O. seriata, 

 Bowbk., the fibres are said to be provided only with echinating 

 spicules. In the species described in the present paper the 

 echinating spicules are relatively few in number and, to 

 some extent, accidental in the occurrence ; they are, in 

 fact, precisely analagous to the spicules (of common 

 occurrence in the genus Clathria) which in the case of 

 C. partita I have refened to as "quasi-echinating" spi- 

 cules. That such spicules are, in some cases at least, 

 to be regarded as, in a sense, accidental, is evident from 

 the following considerations. (i.) In the species in which 

 these occur, the (principal) spicules are not confined to the 

 fibres only, but also occur in the ground substance ; it is quite 

 to be expected, therefore, that some proportion of them 

 should be found to occupy an intermediate situation, i.e., 

 partly within, and partly projecting from the fibre, (ii.) The 

 formation of spicules at the growing-point of the fibre pre- 

 cedes their envelopment by spongin, and since these terminal 

 spicules are often spread penicillately, it follows that outlying 



1 Kirkpatrick— Nat. Antarctic Exped., iv., 1908, Tetraxonida, p. 25. 



2 Vide pp. 137, 138. 



