778 



MR. A. G. THACKER OX 



[June 16, 



a true oscular crown, but an oscular rim or peristome is present ; 

 this varies very much in size, in some specimens being as short as 

 1 mm., or even less, whilst in others it reaches the enormous 

 length of 7 mm. The thickness of the body- wall varies from 

 1 to 2"5 mm., and the maximum diameter of the central gastral 

 cavity is 3 mm. The canal -system is of the form usual in the 

 genus ; the flagellate chambers are spherical or sac-shaped and are 

 rather large, having a maximum diameter of 0'09 mm. The 

 incurrent and excurrent canals have a maximum width of 0-25 mm. 

 The width of the dermal cortex is O'l mm. and that of the gastral 

 cortex 0"06 mm. 



The Skeleton consists of the following elements : — (1) of middle- 

 sized triradiates of the parenchyma, (2) of small triradiates of the 

 dermal cortex, (3) of gastral quadrii-adiates, (4) of large oxea, 

 three times as wide as the parenchymal triradiates, and (5) of 

 minute oxea. 



The main mass of the skeleton is made up by the middle-sized 

 triradiates of the parenchyma (text-fig. 165, a). These vary some- 

 what in shape and size, but are usually sub-regular with rays 

 0"25 by 0"035 mm. Not infrequently they are slightly sagittal 

 with the basal ray shorter than the lateral rays. The rays are 

 shai-ply pointed. 



Text-fig. 165. 



Spicules from JLeucandra crosslandi. 



a = Parenchymal triradiates X 120. b = Dermal triradiates X 120. c = Gastral 

 quadnradiates X 120. d = Large oxeotes X 24. e = Minute oxeotes X 120. 



The dermal cortex consists of a mass of slender-rayed sagittal 

 triradiates ; the lateral rays spread widely at an angle of from 

 140° to 160°, and are from twice to three times as long as 

 the basal ray (text-fig. 165, h). A typical spicule of this kind 

 gave the following measurements -.—Length of lateral rays 

 0-18 mm. ; length of basal ray 0-07 mm. ; thickness of all rays 

 at base 0'012 mm. The rays are sometimes considerably more 

 slender than this. 



The skeleton of the gastral cortex consists of sagittal quadri- 



