HYALONEMA (HYALONEMA) AGASSIZI. - 197 
drew (by the method already described) Figure 7, in which the relative 
frequency of the small micramphidises of various lengths of all the four forms is 
represented. 
The above curves, expressing the relative frequency of the small micramphi- 
dises of different lengths in the six forms, are based on 381 measurements. All 
have one main elevation; those of forms A, C, and E have one secondary eleva- 
tion, the curves of forms B and F have two. The main elevations of the forms 
A, C, and F correspond to amphidise-lengths of about 18.4 u, those of forms B 
‘and D to amphidise-lengths of about 20.1 u, those of form E to amphidisc- 
lengths of about 22.2 yu. 
The first and principal secondary elevation of form F, which is very con- 
siderable, coincides with the main elevation of form E at about 22.2 uw. The 
first secondary elevation of form B, which is quite insignificant, lies at about 
24.4 yu. The first secondary elevation of form E and the second secondary 
elevation of form F, which are both very well-pronounced, lie at about 26.8 x. 
The single secondary elevation of form C, which is inconsiderable, is situated 
at about 29.5 u. The second secondary elevation of form B and the single 
secondary elevation of form A both lie at about 32.5 ». The former of these is 
very well-pronounced, the latter insignificant. 
These curves clearly show that the small micramphidises of forms A, C, 
and F are on the whole relatively small, those of forms B and D intermediate, 
and those of form E relatively large, and further that all the six forms differ in 
respect to the range and character of the variation of the length of their small 
micramphidiscs. 
The description given above shows these sponges to be so similar that there 
can be no doubt about their belonging to one and the same species. They differ, 
however, more or less by their external shape, the structure of their gastral cavity, 
and the shape and size of their spicules. The variable spicule-characters which 
could be accurately ascertained in a sufficient number of spicules in all the forms 
are: — the length and maximum thickness (together with the spines) of the distal 
ray of the dermal pinules and gastral cone-pinules, the nature of the spinulation 
of the former, the diameter of the microhexactines, and the length of the large 
macramphidises and small micramphidises. In the following discussion I have 
considered only these spicule-dimensions, the shape of the sponge, and its gastral 
cavity. 
The specimens from Station 4651 and 4656 and some of the specimens from 
Station 4742 are massive, spindle-, pear-, top-, or club-shaped, the specimens from 
