SCYPHIDIUM LONGISPINA. 25 



Penlactinic hypodermaUa seem to l)e confined in their distri- 

 bution to the upper part of the l)ody. Here they are in places 

 not uucommon, especially on the conical hillocks. I have been 

 unable to detect any regularity in the mode of their relative 

 arrangement. They are never very large ; the largest I have 

 picked out measured : length of paratangential ray, 1.5 mm.; 

 that of the unpaired proximal ray, 5 mm ; thickness of rnys 

 near the center, oo !>. But the majority are considerably smaller. 

 The paratangential rays, which taper outwards to a sharp point, 

 are either regularly cruciately or more or less paratropally dis- 

 posed. The latter form arises as the result of some strong diac- 

 tinic prostalia in immediate proximity excercising a pressure in 

 a lateral direction upon the paratangentials, pushing these away 

 from them and thus widely opening one of the four angles which 

 otherwise would all be right-angled. In some of the spicules, 

 the rays are all perfectly smooth ; in others, the paratangentials 

 present a finely shagreen-like surface (PI. II., fig. 3), caused by 

 the same minute and thickly set processes which I have met 

 with on certain hypodermalia of Lanuginella pupa (p. 9). The 

 proximal ray, as also that part of the diactinic prostalia which 

 dips into the sponge-wall, is accomjjanied with comitalia of the 

 usnal appearance. 



As before mentioned, isolated pentactinic hypodermalia may 

 project outwards, generally in association w^ith the diactinic 

 prostalia on or near the apex of the external hillocks (PI. IL, 

 fig. 10). The pentactinic prostalia, unlike the other kind, are 

 quite inconspicuous. 



As rare abnormalities of the liypodermalia under considera- 

 tion, I may mention a case in which a distal sixth ray was 

 present as a short rudiment, and another case in which two of 



