ME. A. DENDT ON WEST-INDIAN CHALININE SPONGES. 357 



upright, cylindrical, thick-walled tubes, united together in an irregular basal mass and 

 also united laterally in places by the development of horizontal trabeculse of tissue or 

 by direct fusion of adjacent tubes. 



The height of the entire specimen (PI. LXII. fig. 2) is 24 centim., and the breadth 

 about 30 centim. The tubes are not of the same diameter all the way up, but narrow 

 somewhat suddenly at a distance of about 6 centim. from the top : the diameter of the 

 different tubes varies considerably ; that of the orifice of the tubes ranges from 6 millim. 

 (in the case of a young branch) to about 3'5 centim. (in the case of two tubes which 

 have completely fused and have a common aperture), while the average diameter of the 

 orifice in an ordinary full-grown tube may be taken as about 1'5 to 2 centim. The 

 thickness of the walls of the tube averages about 6 millim. The outer surface is smooth 

 but uneven, the tubes being irregularly swollen in some parts and constricted in others. 

 The colour of the specimen (diy) is clear, pale yellow, audits texture is firm but elastic. 

 The true oscula are small, round openings, abundantly scattered over the inner walls of 

 the tubes. 



The main skeleton (PI. LVIII. figs. 1, la) is a beautifully regular and symmetrical, 

 rectangular and close-meshed reticulation of stout horny fibre, composed as usual of 

 primary fibres running vertically to the surface, and secondary fibres crossing them at 

 right angles. The primaries average about 0'058 millim. in diameter, and the 

 secondaries but little less. The fibres contain a few very small and slender vestigial 

 spicules (PI. LVIII. fig. la), apparently on the verge of complete disappearance; these 

 are much more abundant in the primary than in the secondary lines, as is usually the case. 



The dermal skeleton on the outer surface of the tubes is represented by a poly- 

 gonally meshed reticulation of stout, horny fibre, not really distinct from the underlying 

 main skeleton. 



The spicules are represented by mere traces of slender oxea, which have been almost 

 completely absorbed. 



This beautiful species is characterized chiefly by the large amount of spongin, and 

 the corresponding almost entire absence of spicules of the fibre, thus forming a striking 

 contrast to Siphonochalina spiculosa, mihi, which bears a considerable external resem- 

 blance to it. 



Locality. Nassau, Bahamas. 



Genus Spinosella, Vosmaer. 



1864. Tuba, Duohassaing and Miclielotti, "Spongiaires de ]aMerCaraibe,"NatuurkundigeVerhande- 

 lingen van de hoUandsche Maatschappij der AVetenschappen te Haarlem, 1864, p. 44. 



1870. Siphonochalina, pars, Schmidt, Grundziige eiuer Spongien- Fauna des atlantiscben Gebietes, 

 p. 33. 



1885. Spinosella, Vosmaer, Bronn's ' Klassen und Ordnungen des Tliierreichs,' Porifera, p. 342. 



Diagnosis. Simple or branched, tubular Chalininae, having the inner surface of the 

 tubes smooth, and the outer surface covered with spines, warts, or prominent ridges. 

 VOL. XII. — PAKT X. No. 2. — April, 1890. 3 f 



