EEPORT ON THE KERATOSA. 55 



permeating its body, the external shape of the animal and particularly its shagreen- 

 like surface, its skeleton (more compact than, but not nearly so hard as, that of Caco- 

 spongia mollior) recalls that of a Euspongia rather than that of a Cacospongia. 



If now this species, as regards the property of its skeleton, were a typical Euspongia, 

 the question as to its systematic place would be still more difficult ; one classifier might 

 place it in the Euspongice, another, and on grounds of equal validity, among the Hippo- 

 spongicB. Now the species in question is neither a Euspongia nor a Cacospongia, nor a 

 typical Hippospongia ; but since one of the main characters of Hlppospongia is very 

 characteristic of this specimen, the most logical proceeding will be, I think, to group it in 

 this latter genus. For my own part I do not doubt that the species in question, be it referred 

 to Hippospongia or Euspongia, will still remain a good species, and I shall be quite content 

 if my description prove sufficient for future recognition. In order to render it more com- 

 plete I add the following details. The average diameter of the primary fibres reaches 0"12 

 mm., that of the secondary fibres being on an average only 0'028 mm.; the latter are 

 nearly all quite free from any foreign enclosures ; the first-mentioned, however, are so full 

 of them that their surface is of a rather angular character, owing to the fact that these 

 foreign bodies lie not only in the central part of the fibres but also in their j^eripheral 

 portions, projecting outwards and thus rendering the surface of the fibres uneven. It is 

 in this form that I have found, hand in hand with normal flagellated chambers, chambers 

 devoid of any special camera! canaliculis, although in other details its internal organisa- 

 tion presents no deviations from that, for instance, of Euspongia officinalis. The 

 specimen proved to be sterile. 



Colour. — Soft parts and outer surface pale yellowish-white, skeleton straw-yellow. 



ifa&itoi.— Station 186, September 8, 1874, lat. 10° 30' S., long. 142° 18' E., depth 

 8 fathoms, coral mud. 



Hippospongia mauritiana (PI. VI. fig. 3). 



Spongia lapidescens, Duchassaing de Fonbressin et iliclielotti ; subspecies mauritiana, Hyatt, 

 Revision, &c., vol. ii. p. 527. 



There can be scarcely any doubt that the three specimens of the collection now under 

 consideration are to be referred to Hyatt's Spongia lapidescens, subspecies mauritiana. 

 His description is very good and detailed, and the form itself, owing to the density of 

 its skeleton, admits of a very clear definition. But what appears to me very strange is 

 that Hyatt still finds it possible to distinguish in its skeleton primary and secondary 

 fibres. I find them all approximately of the same size ; of course the bundles of parallel 

 fibres projecting from the outer surface are directed vertically, but seeing that they are 

 not united one with another by smaller horizontal fibres, and that they do not difl'er in 

 thickness from other fibres of the skeleton, I see absolutely no grounds for regarding 



