SPONGES— HALLMANN. j r ^ 



iargest measure about J70 x 4/^. Beneath the surface of the 

 sponge and running perpendicularly towards it are numerous 

 wispy strands of the same spicules. With regard to the ar- 

 rangement of the skeleton Microciona scahida stands precisely 

 in the same relation to the type-species of Stylotellupsis — .S'. 

 amabilis'^ — as does Crclla incfustans var. levis to C. incrustans 

 var. puniila ; and, in compliance with the present scheme of 

 classification, should accordingly be placed in 'Ihiele's genus. 



Another interesting species whose systematic position ap- 

 pears to be somewhere in the vicinity of Clathrissa and Stylo- 

 tellopsis is Echinodictyum ridleyi, 'Dendy.2 The skeleton is 

 made up almost entirely of slender longitudinal wispy fibres 

 and is consequently rather of the dendritic than of the reticu- 

 late type. Accompanying the slender oxeote or rather torno- 

 loxeote spicules (size about 270 x 4^) which chiefly compose 

 thiese fibres, are a few conical smooth styli (190 x 7 n) and 

 .acanthostyles (100 x 6ji), both kinds of which occasionally 

 project from the fibres somewhat in the manner of echinating 

 spicules. There are no microscleres. ihe diactinal spicules 

 of the fibres exidently correspond to the auxiliary megascleres 

 of normal Myxillina\ and the species accordingly possesses 

 no claim to a place in the genus Echinodictyum in which the 

 fibres are formed by principal spicules and in which the aux- 

 iliary spicules are represented by interstitial or dermal styli. 

 Also, it is scarcely to be doubted that the smooth conical styli 

 are homologues of the larger acanthostyles of Clathrissa 

 arbuscida, Stylotellopsis amabilis and S. {Microciona) scahida 

 and to the principal styli of normal Myxillina?. C. arbuscula 

 and S. amabilis differ in generic characters mainly in this 

 respect, that in the latter the auxiliary megascleres are pointed 

 at one end only, whilst in the former they are pointed at both 

 ends. But this difference cannot be regarded as of much im- 

 portance since the probability is that the tornotoxea of C. 

 arbuscida are, strictly speaking, just as truly monactinal as 

 the tornostrongyles of S. amabilis. Consequently Echino- 

 dictyum ridleyi owing to the perfect smoothness of its prin- 

 cipal styli, stands farther remo\ed from either of the two last 

 mentioned species than these do from each other, and is thus 

 fairly entitled to distinction under a new generic name. In 

 E. ridleyi, as already mentioned, the principal and accessory 

 styli are both comparatively rare in their occurrence ; if the 

 former spicules were to disappear, such a species as Echino- 

 dictyum spongiosum, Dendy,^ would result; whilst if both 

 kinds were lost, there would be scarcely anything in the struc- 



1 Thiele— Fauna Chilensis, Bd. 3, p. 456, fig. 72 a-d. 



2 Dendy— Proc. Eoy. Soc. Vict., viii., 1896, p. 44. 



3 Dendy— Proc. Roy. Soc. Vict., viii., 1896 p. 45. 



