EUPLECTELLA. 49 



of prostalia are to l)e distinguished : Firstly, the distallj directed 

 ray of pentactin or hexactin parenchymal principalin, already 

 noticed as occurring in the circular and longitudinal skeletal 

 beams of certain species. Secondly, slender oxydiactins swollen 

 at the spicular center ; these occur usually comitalia-like along 

 with the radial rays of dermalia and are often protruded exter- 

 nally in bristle-like bundles, especially at the free edge of the 

 cuff and of certain parietal ledges. Thirdly, the basalia or the 

 anchoring spicules, which are by far the most conspicuous and 

 important of all the prostalia. 



The basalia are as a rule pronged thread-like diactins, the 

 distal ray of which is exceedingly short in comparison with the 

 excessively prolonged proximal ra}^, but is terminally provided 

 with a miter-shaped knob, the anchor-head, supplied with a 

 whorl of retro verted anchor- teeth (PI. II, fig. 16 ; &c.). The 

 latter are, as has been enunciated by previous writers, to be 

 regarded as secondary prongs — not rays. A short distance above 

 the head is the spicular center, at once recognizable by the axial 

 cross within. In the head, the inferior extremity of the axial 

 filament is either irregularly swollen or split in a penicillate 

 manner into a few diverging branches. From about the spicular 

 center upwards for a considerable length, the anchor-shaft is 

 armed with barb-like prong«, arranged in a broken spiral line 

 but at times disposed somewhat irregularly. The upper portion 

 of the shaft is perfectly smooth and thins out superiorly to a 

 fine point. The above basalia are grouped in bundles run- 

 ning along, and in direct apposition with, the external side of the 

 longitudinal skeletal beams in the lower part of the sponge-wall. 

 In forming the basal tuft, the bundles emerge from the parietal 

 tissues in a circle around the inferior end of the lateral wall. 



