456 DR. J. S. BOWERBANK ON THE SPONGILLlDiE. [NoV. 24, 



form, terminating at the small end in a short, cylindrical, tubular 

 foramen, the length of the tube beyond the outer surface of the ova- 

 rium being about equal to its diameter. The foramen appears to be 

 most frequently at the distal end of the envelope as regards its at- 

 tachment to the skeleton. The thickness of the wall of the ovarium 

 appears to be determined by the length of the boletiform spicula, 

 the outer convex surface of which forms the inner surface of the 

 ovary, while the small clavate or stellate end is seen either imme- 

 diately beneath the outer surface of the ovary or slightly projecting 

 beyond it. In the living condition it is probable the former would 

 be its natural position. 



There are several singular points in the structure of this species. 

 I have never found before among the Sponr/illiclxs either the ovary 

 oval or the foramen distinctly projected above its surface ; and it is 

 the first occurrence of the singular and beautiful boletiform spicula. 



Spongilla rectjrvata, Bowerbank. 



Sponge sessile, coating surface even, smooth. Oscula inconspi- 

 cuous, numerous, simple, dispersed. Pores inconspicuous. Dermal 

 membrane thin, translucent, aspiculous. Skeleton-spicula cylindrical, 

 short, and stout. Ovaries globose ; surface even, pitted, furnished 

 with spicula : external spicula multihamate-birotulate ; hami of the 

 rotulse stout, attenuating, much recurved ; shaft cylindrical : internal 

 spicula boletiform ; proximal or large extremity irregularly circular, 

 flat, or very slightly convex outwardly, thin, margin entire ; small 

 or distal extremity lentiform ; shaft attenuating from the larger to 

 the smaller extremity. 



Colour, dried state, light brown. 



Hab. Villa Nova, River Amazon. 



Examined in the dried state. 



This little species was found closely embracing about half of one 

 of the small stems of a tree, which a full-sized specimen of Spongilla 

 reticulata covered for about G inches in length ; the stem rather ex- 

 ceeded one-eighth of an inch in diameter ; and the large Sponge in its 

 growth has evidently partially grown over the smaller one, which is 

 not more than one-third of a line in thickness. The best specimen 

 I possess was detached, and was found loose in the paper in which 

 the whole of the specimens I received from Mr. Bates were packed ; 

 it is about three-fourths of an inch in length ; and the Sponge when 

 whole, judging from the length of the detached portions, may have 

 been about 3 inches in length. In the largest detached piece there 

 were more than forty ovaria imbedded in one stratum at the base of 

 the Sponge, with the foramen of the greater part of them downwards. 

 The diameter of an average-sized one was -^ inch. We may there- 

 fore fairly infer, although the Sponge is so thin, that it is in an adult 

 condition. Notwithstanding its length, it does not appear to be in 

 the habit of entirely surrounding the stem on which it is seated, as 

 it had done so in one small spot only. 



The oscula are not visible without the aid of a lens ; they are vari- 

 ous iu suG, and rather numerous. The dermal membrane is thin and 



