88 



cula, arranged in irregular, longitudinal rows protrude. Some of these processes, 

 particularly those of the lower end of the body, are extended to form tubes, 

 terminally irregularly truncate, 1-2 cm. long and 3-4 mm. broad. Most of 

 them however, particulai'ly those of the upper part of the body, are much 

 shorter, and terminate with a hemispherical, dome-shaped apex. It is 

 particularly to be remarked that, both in the " Investigator " specimens and in 

 Gray's figure of the type specimen, these diverticula gradually decrease in size 

 towards the upper end of the body. The lowest diverticula are always the 

 longest, and the uppermost ones, situated just below the oscular margin, always 

 the shortest. The latter usually appear as slight, rounded elevations of the 

 outer surface (pi. XV, f. 1). In the upper and central part of the body these 

 diverticula are usually so close together as to be nearly in contact with each other. 

 Further down the diverticula are not so numerous, and at the narrow lower end 

 itself are generally entirely absent. Most of the diverticula have a perfora- 

 tion, more or less round and 1-2 mm. wide, at, or a little below the apex. 

 Exceptionally, here and there one is met with without such a perforation. 



The dictyonal net, which forms a regular and uniform hexagonal honey- 

 comb ; the hexactine dictyonalia, which are joined in a peculiar manner to form a 

 rather irregular net- or lattice-work with triangular meshes and irregularly 

 polyradiate nodes; and the slender, tuberculous, cylindincal processes which 

 protrude from the dermal and gastral surface; all accord with the typical char- 

 acters of the genus Aphrocallistes. 



I find the dictyonal net of the younger, central aud upper regions of the 

 body thin, the beams composing it nearly quite smooth ,and the nodes but very 

 slightly or not at all thickened, and only sparsely covered with small, pointed 

 tubercles. Only at the dermal and gastral margins, on t;he surfaces bounding 

 the honeycomb-cavities, the pointed tubercles of the beams < and of most of the 

 nodes are .stouter and more numerous. In the lower, older regions of all the 

 specimens the dictyonal network forms a thicker layer, is 'stronger and covered 

 nearly entirely with numerous, stout, pointed tubercle.'S. The nodes are here, 

 particularly on the dermal and gastral si;rface, considerr.ibly thickened and appear 

 as round, generally clearly defined inflations. 



The differences in the developement of the small, \pointed tubercles on the 

 beams and nodes of the dictyonal net and of the thicl'iness of the nodes them- 

 selves, can therefore not be considered as distinctive spec^ific features. It is not 

 to be denied however, that the constancy and degree of developement of these 

 peculiarities, although dependent on the age of the specfmen, may occasionally 

 attain the importance of specific characters. 



The dermalig. are slender hexactines, with free distal ra^js 100-200 t^ long, 

 terminally sometimes thickened in a club-shaped manner and ciovered with slender 

 spines or thorns of medium length which diverge obliquely ai.\d are curved to- 



