HYALONEMA (HYALONEMA) AGASSIZI. 197 



drew (by the method already described) Figure 7, in which the relative 

 frequency of the small micramphidiscs of various lengths of all the four forms is 

 represented. 



The above curves, expressing the relative frequency of the small micramphi- 

 discs 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 cm-ves of forms B and F have two. The main elevations of the forms 

 A, C, and F correspond to amphidisc-lengths of about 18.4 m, those of forms B 

 and D to amphidisc-lengths of about 20.1 m, those of form E to amphidisc- 

 lengths of about 22.2 ix. 



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 m- The 

 first secondary elevation of form B, which is quite insignificant, lies at about 

 24.4 fi. The first secondary elevation of forrii E and the second secondary 

 elevation of form F, which are both very well-pronounced, lie at about 26.8 m- 

 The single secondary elevation of form C, which is inconsiderable, is situated 

 at about 29.5 ix. The second secondary elevation of form B and the single 

 secondary elevation of form A both lie at about 32.5 m- The former of these is 

 very well-pronounced, the latter insignificant. 



These curves clearly show that the small micramphidiscs 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 

 macramphidiscs and small micramphidiscs. 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 



