400 HYATT'S REVISION OF THE 



Tlie J;intlielli(l;i3 are so very similar in form and in the size and asjaect of the fibres, to both 

 Antipathes and Gorgonia among the Corals, that when no animal matter is left upon the 

 branches it is very ditBcult to separate them from the last named. On the other hand, we 

 have the finest and most attenuated fibres and typical sponge structure in the fistular forms 

 of the genus Spongia. So little is known of the purely anatomical characteristics of the 

 internal joarts of most singular forms, such as Jauthella, that it would hardly be safe to 

 attempt any generalization in this direction. 



Sub-order APLYSINJE Hyatt. 

 Sub-oi-cler IV Bowerbank. 



Though Schmidt is disposed to discourage the use of a distinct name for this group, I 

 find myself obliged to admit the hollow-fibred species to the rank of a distinct subdivision 

 of the order Keratosa. The Aplysinte appear to me a perfectly natural and very easily dis- 

 tinguished group. The skeleton is composed of anastomosing horny fibres, which are 

 typically hollow, though not infrequently filled up by a granular deposit. This filling is 

 generally of a light yellow color, except in Aplysina aurea, (in which it is absent, its place 

 being apparently supplied by a thin membrane), and the fibres are therefore either 

 transparent, or black and opaque. The enormous compound fibres of Janthella have 

 neither membrane or yellow matter in the interior, and are also not continuously hollow. 

 The horny matter is laid on in concentric layers, and these are quite loosely connected. 

 Thus the walls of the inner tubes seem sometimes to have shrunk in the dried specimens 

 until they touched and entirely filled the centre with a solid core ; whether this also 

 occurs in the living animal I cannot say. The horny material is deposited in concentric 

 layers from without, and in some species, as in A. ceUiiIosa, this deposition appears to 

 continue indefinitely, the fibres becoming in course of time exceedingly broad. Usually 

 also the terminations of the fibres near the exterior have much thinner walls than is 

 found in the interior, the concentric deposits being thicker in the older portions of the 

 sponge. This, in dried specimens, causes the collapse of the terminations of the branches 

 and their peculiar irregular twisted aspect and almost black color in some species.^ The 

 fibres of Verongia are exceptions to this rule ; they remain of about the same rotund form 

 in all pai'ts. The variations appear to be in the extreme thickness of the walls of the older 

 fibres, though this increase is never so excessive as in Ajjlysina celhilosa.^ 



DENDROSPONGIADJi:. 



This family is characterized by the irregular anastomosis of the fibres of the skeleton, 

 their rotund form, and the thickness of the horny walls. 



Dendrospongia Hyatt. 

 Aplysina (pars) Schmidt. 



One specimen from the Museum of Comparative Zoology is named by Schmidt as Aply- 

 sina oirophoha ?. It is fistulose and not very different outwardly from the true A. trroj^hoha, 

 though the surface is much rougher and shows coarse spiniform projections in place of the 



iPl. 13, fi^. 7. JPI. 13, fi<r. 19. 



