38 C. F. JENKIN. 



Spicules (Fig. 119). 

 Oxea. There are two sorts of Oxea : 



(a) Enormous straight projecting oxea more than 15 mm. long x 36 p. to 43 p. 



thick. The inner end tapers gradually to a very sharp point, the outer 

 end is hastate. 



(b) Minute irregularly bent hastate oxea, some spined, some smooth, from the 



gastral and dermal layers, 80ft to 160 p. long X 6 /A thick. 



The Triradiates are of one sort : 



(c) Alate triradiates from the body-wall and dermal layer. Basal rays straight, 



tapering uniformly to a sharp point, 220 p. to 700 p. long x 10 p. to 16 p. 

 thick. Paired rays equal, nearly straight, 170 p, to 300 p, long X 12 p. to 

 14 p. thick. Oral angle 135 to 155. 



(d) Chiactines. Basal ray straight, tapering uniformly to a sharp point from 

 600 p, to 1120j, long X 10 p. to 16 p. thick. Paired rays equal, straight, 

 tapering to a sharp point, 240 p. long x 13 p. thick. Oral angle 155 to 

 160. Slightly folded, angle of fold 175 to 150. Apical ray straight, 

 slender, sharply pointed, 140/i to 220 p. long X 8 p. to 16 p, thick, set-off 

 small ; angle between apical ray and basal ray 170 to 180. 



MEGAPOGON RARIPILUS. 

 (Plate XXXVI., Figs. 120-124.) 



There are three specimens of this new species in the collection. The natural shape 

 appears to be that of a straight tube, enclosing the gastral cavity, slightly thicker in 

 the middle and circular in section. The lower end is closed very squarely, and the 

 upper terminates in an oscule without a collar. The largest specimen, which is much 

 distorted, is 30 mm. x 11 mm. ; the next, which has the shape described above, is 

 19 mm. x 4 mm., and the smallest specimen 2 mm. x 1 mm. They are white as 

 preserved in alcohol, their surface is hispid. 



The structure of the thick body- walls is shown in Fig. 122. 



Canal System. The stout dermal cortex (Fig. 124) is pierced by small 

 ostia leading into small incurrent chambers, from these run incurrent canals branching 

 and getting smaller as they approach the gastral cavity. The excurrent canals are 

 connected in groups of three or four to excurrent chambers which open into the gastral 

 cavity through large ports. 



Skeleton. The body skeleton consists of the chiactines, amongst which are a few 

 large subgastral triradiates and a few scattered small triradiates ; the basal rays of the 

 latter often project beyond the dermis. There are also dense tufts of hair spicules with 

 a few stout bent oxea among them, which project and make the surface hispid. There 

 are minute spined hastate oxea scattered all through the body. There is no gastral 



