218 PROCEEDINGS OF THE ACADEMY OF [1887. 



Gemmules ovoid, rather numerous, approximating to one another 

 in groups of varying numbers, surrounded upon the upper side by 

 a rather sparse capsule of skeleton spicules, which become very nu- 

 merous below, particularly around the cii'cumference, where they 

 buttress and elevate the gemmule above the firm basal membrane 

 of the sponge. Foraminal apertures uniformly downward. The 

 chitinous coat is covered by a very thin crust in which a compact 

 series of short birotulates is embedded. 



Skeleton spicules cylindrical, short and rather stout, slightly and 

 nearly uniformly bent ; terminations rounded ; entirely spined ; 

 spines, low-conical, acute, more conspicuous ujDon the outer curves of 

 the spicules. 



No dermals seen. 



Gemmule spicules birotulates with entire circular margins and 

 extremely short shafts ; rotules flat. 



Meas. Average length of skeleton spicule about 0'0036 inches. 

 Diameter of rotules 0'00045 inches ; height of birotulate 0"0002. 



Loc. Beni river. East Bolivia; collected by Dr. H. H. Rusby. 



(4) Meyenia minuta, n. sp. 



Sjionge as seen minute, encrusting, relatively compact ; the spic- 

 ules non-fasciculated and without definite arrangement. 



Gemmules in the dried state faintly suggested by the curvatures 

 of the upper surface of the sponge ; rather numerous, spherical, very 

 small, (about one fourth the average diameter of those of other spe- 

 cies), a thin granular crust embedding birotulates that are no small- 

 er than those of the three previous species. 



Skeleton spicules slender, cylindrical but gradually sharp-pointed 

 vsntirely spined ; spines conical, acute. 



Dermal or flesh spicules wanting. 



<jemmule-birotulates short, shafts smooth, thinnest at the centre ; 

 TOtules nearly equal ; margins entire, slightly reflexed, more partic- 

 <ularly that of the outer ro.tule which thus becomes cup-shaped. 



Meas. Diameter of gemmules about 0'005 inches; a line of ten or 

 twelve of its birotulates only, being found along its semi-equator. 



JSah. Found encrusting a leaf belonging to the stem uj)on which 

 a mass of Parmula brownii, var. had formed. 



Loc. Collected by Dr. H. H. Rusby along a small branch of the 

 river Beni in Eastern Bolivia, S. A. (See also P. brownii.) 



This is the most minute mature sponge that I have ever met with. 

 The masses, even, can hardly be said to be visible to the naked eye 



