ME. A. DENDY ON WEST-INDIAN CHALININE SPONGES. 367 



stout horny fibre, but in parts a distinctly rectangular arrangement is visible. Both 

 the primary and secondary lines are cored by oxeote spicules, which are fairly abundant 

 in the primary fibres, but scarce in the secondaries. The longitudinal veins above 

 mentioned are, as in the case of Spinosella sororia, due to local concentrations of the 

 skeleton reticulation. The fibres of the skeleton average in diameter about 0*044 millim., 

 and there is no noteworthy difference between the primaries and secondaries in this 

 respect. 



A special dermal skeleton, distinguishable from the underlying main skeleton, 

 appears, as usual, to be developed only on the outside of the tubes. It consists of an 

 irregularly, polygonally meshed reticulation of slender horny fibre cored by fairly abun- 

 dant oxeote spicules. 



The spicules are slightly curved, sharp-pointed oxea, measuring about 0T by 0'0045 

 millim., when found perfect ; a large proportion of them, however, appear to be under- 

 going absorption and are much slenderer. A few spicules occur scattered outside of the 

 fibres. 



It will be seen that in most respects this species comes very near to the typical forms 

 of Spinosella sororia, but it is at once marked off from that species, and, indeed, from 

 all other species of Chalininse with which I am acquainted, by the presence of the very- 

 remarkable diaphragms in the orifices of the tubes. 



Locality. Bahamas. 



III. EXPLANATION OF THE PLATES. 



PLATE LVIII. 



Fig. 1. Siphonochalina ceratosa. Portion of main skeleton as seen in section at right 

 angles to the surface; X25. p, primary fibres; s, secondaiy fibres. 



Fig. la. Siphonochalina ceratosa. Portion of the above; Xll5. p, primary fibres; 

 s, secondary fibres ; sp>, spicules. 



Fig. 2. Siphonochalina spiculosa. Portion of main skeleton as seen in section at right 

 angles to the surface ; X 25. 



Fig. 2 a. Siphonochalina spiculosa. Portion of the above; Xllo. 



Fig. 3. Pachychalina variabilis. Portion of main skeleton as seen in section at right 

 angles to the surface ; X 25. 



Fig. 4. Siphonochalina procumbens. Portion of main skeleton as seen in section at 

 right angles to the surface ; X 25. p, primary fibres ; s, secondary fibres, 



Fig. 5. Spinosella plicifera. Portion of main skeleton as seen in section at right 

 angles to the surface ; X 25. p, primary fibres ; s, secondary fibres ; a, reti- 

 culation of very fine fibres lying between the stouter ones. 



3g2 



