36 C. F. JENKIN. 



composed of irregularly scattered radiate spicules, but it always has regularly placed 

 suhgastral chiactines. 



The above only differs from Dendy's definition of Leucavdra by an alteration in 

 the last sentence. 



This genus contains five species, four new, and Polejaeff's " Leuconia crucifera " 

 {Megapogon cruciferus), which is now transferred to it. 



All the species have well-marked gastral cavities, but no gastral skeleton 

 proper. The spiculation in all the species is very similar. The size and shape 

 of the flagellated chambers is very variable ; they «re sometimes so long as to 

 resemble the radial chambers typical of Grantia or Achramorpha, and at other times 

 they are spherical. 



The close similarity between Megapogon cruciferus found at the Azores and the 

 new species from the Antarctic is remarkable. It is noteworthy that Megapogon 

 cruciferus was dredged from a great depth, 450 fathoms. The temperature of the sea 

 was not measured at the station where it was found, but judging from the 

 temperatures measured at neighbouring stations it must have been about 47° F. at 

 the bottom. It is possible that successive larvae of this sponge may have travelled in 

 cool water at great depths all the way from the Antarctic to the Azores. 



MEaAPOGON CRUCIFERUS Pol. 



(Plate XXXVL, Fig. 114.) 

 Leuconia crucifera Pol6jae£F (4), p. 60. 



The following description is abstracted from Polejaeff's (4). Only a fragment 

 of the inferior part of the sponge was found. The outer surface is bristly, the inner 

 slightly roughened by the apical rays of the gastric quadriradiate spicules [chiactines]. 

 These are all more or less cruciform, all the rays lying in the same or almost the same 

 plane. By this characteristic the species can be very easily distinguished from all 

 other Leuconidse. Leuconia crucifera and Leuconia hlanca are of peculiar interest, as 

 forms inhabiting the greatest depth (450 fathoms) from which Calcarea have been 

 hitherto obtained. 



Skeleton. — The skeleton consists of gastral quadriradiates [chiactines], of 

 parenchymal triradiates [of minute spined oxea *], of dermal triradiates and of stout 

 acerate spicules, piercing the parenchyma obliquely and projecting with their free end 

 from the outer surface, and of slender acerate spicules scattered here and there on the 

 outer surface in small bundles. The spicules (omitting the hair spicules) are shown in 

 Fig. 114 drawn from spicule preparations made by the author. For description and 

 dimensions see (4). 



* These spicules were overlooked by PoWjaeff. They are included in the new drawing of the spicules. 



