3G4 ME. A. DE>^DT ON WEST-IXDIAX CHALININE SPONGES. 



All three specimens have the same light fawn-colour, and all three the same kind of 

 acerate spicule ; that of T.plicifera is 18 by f-6000ths inch, and that of T. eschrichfii 

 18 by -|~6000ths inch, in their greatest dimensions respectively, so that it is finest in 

 the thickest fibre, but very scanty in all three. 



"Each specimen presents a young one at its base, which is blind at the free end (that 

 is, without orifice)." 



In the specimen from the Bahamas which I am about to describe, 1 have not 

 succeeded in detecting any spicules at all ; but, on the other hand, there is in the 

 collection of the British Museum a microscopical preparation labelled in Professor 

 Schmidt's handwriting " TwJaD. et Mich. (^^/c//(?r« ?)," and in this preparation there 

 are traces of spicules in the fibre still quite distinct, but very slender and apparently 

 on the verge of disappearing. 



Whether or not there were spicules in the specimens examined by Duchassaing and 

 Michelotti, we cannot, of course, tell; but in the fragment of the skeleton reticulation 

 figured by them none are visible. 



It might here be urged that we ought to distinguish two species — one with spicules, 

 however few and vestigial, and one without any spicules at all. But it is impossible 

 to draw such a hard-and-fast line in this particular case, which is simply an excellent 

 illustration of the manner in which the spicules gradually disappear as the horny fibre 

 becomes more and more strongly developed ; and it is better to say of the species that 

 the spicules are either present in a vestigial condition, and in very small numbers, or else 

 entirely absent. 



The single specimen in the collection (PI. LX. fig. 1) is 43 centim. in height and 20 

 centim. in greatest breadth ; and the outer surface is thrown into strongly developed 

 transverse folds, while the inner surface is irregularly pitted. Tiie tube is at first single, 

 but at a distance of 12 centim. from the top it bifurcates into two. These two remain 

 connected externally almost up to the margin, but the two apertures are quite distinct. 

 Each aperture is approximately circular and provided with a delicate fringe ; the one 

 measures about 8 centim. in average diameter, the other only about 7'5 centim. The 

 specimen is of a light brownish-yellow colour. 



The skeleton is a very well-developed reticulation of stout horny fibre ; but there 

 appear, as I have already stated, to be no spicules. The main skeleton (PI. LVIII. fig. 5) 

 is, for the most part, very symmctricully arranged, consisting of a rectangularly meshed 

 reticulation of stout primary and secondary fibres. The primary fibres are but little stouter 

 than the secondaries, which latter average about O'OS millim. in diameter. The meshes 

 of the reticulation, when seen in vertical longitudinal sections, appear oblong in shape, the 

 secondary fibres forming the longer side of the oblong. From various points on both 

 primary and secondary fibres of the main skeleton spring much slenderer fibres, which 

 branch and anastomose in an irregular manner, so as to form a kind of additional 

 reticulation spread between the meshes of the principal one. Tlie diameter of these 



