62 THE VOYAGE OF H.M.S. CHALLENGER. 



and a predominance of minute acerate spicules. From this point of view the species 1 

 am going to describe is of particular interest. In the main features of its organisation 

 it does not differ from Leuconia multiformis, Leuconia typica, &c, its cortical layer being- 

 represented by a thin dermal membrane ; but its spicular characters are so strikingly 

 similar to those of Leuconia (Baeiia) saccharata, H., 1 that a close parentage of both 

 these forms is evident ; and Leuconia saccharata, even in spite of its, I must add, very 

 doubtful subdermal cavities, is one of the most typical representatives of our conjectural 

 genus. 



Leuconia ovata is represented in the Challenger collection by one specimen from 

 Christmas Harbour. The specimen is of ovoid form, yet rather compressed, 30 mm. long., 

 18 mm. broad in the middle, its walls 4-5 mm. thick, in the interior half growing 

 gradually thinner towards the free end. Both the surfaces are smooth. As I remarked 

 before, no deviations are to be noticed with respect to the internal organisation ; as in 

 most Leucones, the flagellated chambers are of roundish outline, their diameter - 06 mm. 

 on an average, the pores and vents (gastric openings) of variable size and irregularly 

 disposed. The specimen proved to be sterile. 



Skeleton. — The skeleton consists of minute acerate spicules, coating the gastric and 

 dermal surfaces, of gastric triradiate, of parenchymal triradiate, and of dermal triradiate and 

 quadriradiate spicules. 



Minute acerate spicules. — Some of these are just of the same form, and most of the same 

 dimensions, as the corresponding ones in Leuconia saccharata, every spicule being com- 

 posed of two parts — of a shorter spiny and of a louger smooth ; but while Leuconia 

 saccharata is, according to Hajckel, quite constant to this characteristic form of its 

 minute acerate spicules, those in Leuconia ovata show a considerable variability ; 

 sometimes they are spiny on their whole surface, sometimes, on the contrary, they are 

 smooth in both their parts, sometimes the shorter is smooth and the longer spiny. Also, 

 with respect to the angle formed by their longer and shorter parts, these acerate spicules 

 are inconstant, there being amongst them all possible intermediate stages between such 

 spicules as drawn by Hseckel for his Lcucandra saccharata {loc. cit, pi. xxxviii. fig. 13) and 

 common spindle-shaped acerate spicules. Characteristic of both surfaces, the minute 

 acerate spicules lie in the parenchyma perpendicular to the longitudinal axis of the Sponge, 

 the shorter spiny ends of the dermal acerate spicules being directed centrifugally, those 

 of the gastric spicules eentripetally. 



Gastric triradiate spicules. — These are also of the form and size of the corresponding spicules of 

 Leuconia saccharata, but more variable with respect to the length of their rays, that of the 

 lateral varying from 015 mm. to 03 mm., that of the basal ray from O'OS mm. to 0'2 mm. 

 In most cases the basal ray is J-| as long as the lateral, but occasionally its length reaches, 

 and even surpasses, that of the lateral. Some of them — not many — are provided with a 

 short (0'02 mm. to 0-08 mm.) apical ray. The basal ray of the gastric triradiate spicules 

 1 Kalkschwamme, Bd. ii. \.. 229, Bd. iii. pi. xxxiii. figs. 3a-3e, pi. xxxviii. fig. 13. 



