ME. A. BENDY ON WEST-INDIAN CIIALININE SPONGES. 351 



The first of these two general laws is very clearly demonstrated in the case of 

 Spinosella sororia, D. & M., sp., of which I distinguish three varieties in addition to 

 the typical form (PL LIX. figs. 1, 3 ; PI. LXIII. figs. 1, 2), and in the case of Pachy- 

 chalina variabilis, mihi (PI. LX. fig. 2) ; hut as this will be sufficiently clear from the 

 figures and from the descriptions given in the systematic portion of this paper, I shall 

 not consider the question any further in this place. 



The second law has already been very strongly insisted upon by Mr. Ridley and 

 myself in our Eeport on the Monaxonida collected by H.M.S. ' Challenger,' in which 

 we have endeavoured to show that the so-called " Keratosa " have probably descended, 

 polyphyletically, from several distinct groups of siliceous sponges, amongst which the 

 Chalinina3 figure prominently. The view that the Keratosa have been derived from 

 siliceous sponges has been gradually gaining favour with naturalists for some time past, 

 and is now, I believe, very generally admitted to be correct. But I have nowhere 

 found quite such strong arguments in its favour as amongst the West-Indian Chalininse; 

 for here we can trace in different species of the same genus the gradual degeneration 

 and disappearance of the spicules until we come down to forms like Spinosella 

 maxima, mihi (PL LXI.), and Spinosella plicifera, D. & M. (PL LVIII. fig. 5 ; 

 PL LX. fig. 1), which sometimes still contain traces of the spicules imbedded in the 

 horny fibre, and apparently on the verge of disappearance, while at other times they 

 contain no spicules whatever; and yet the specimens with spicules and those without 

 are specifically indistinguishable. 



It appears that the spicules may persist as vestigial structures long after they have 

 ceased to be of any functional importance, and that they disappear first from the 

 secondary skeleton-fibres. Thus in the genus Siphonoehalina we have S. spiculosa, 

 mihi (PL LVIII. figs. 2, la; PL LXII. fig. 3), with great numbers of well-developed 

 spicules constituting a most important part of the skeleton-fibre, and, on the other 

 hand, S. ceratosa, mihi (PL LVIII. figs. 1, 1 a ; PL LXII. fig. 2), in which the spicules 

 have almost completely vanished ; while Siphonoehalina procumbens, Carter (PL LVIII. 

 fig. 4 ; PL LXII. fig. 1), occupies an intermediate position in this respect, containing 

 several series of fair-sized spicules in the primary fibres and only a sparse single series 

 of similar spicules in the secondaries. 



The classificatory difficulties to which this state of things, leads are obvious. It is, 

 in fact, no longer possible to draw a sharp line of distinction between the Chalininse 

 and the so-called Keratosa ; for different specimens of one and the same species may or 

 may not contain spicules, while at the same time it is probable that a large proportion 

 of the Keratosa have no near connection with the Chalininse at all, but are descended 

 from quite different groups of siliceous sponges L 



Some of these difficulties are well illustrated by a note at the end of Professor 



1 Cf. Ridley and Dendy, Eeport en the Monaxonida collected by H.M.S. ' Challenger,' p. lv et seq. 



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