446 DR. J. S. BOWERBANK ON THE SPONGILLIDiE. [NoV. 24, 



Oscula numerous, small, congregated, elevated, and marginated. 

 Pores conspicuous. Skeleton-spicula acerate, small, short, and 

 stout, rather obtusely terminated. Dermal and interstitial mem- 

 branes pellucid, aspiculous. Ovaria spherical, small ; dermal spi- 

 cula birotulate, minute, short ; shaft cylindrical ; rotulse, margins 

 entire, that of the outer one sometimes exflected, and rarely spicu- 

 lated. 



Colour yellow, with a tint of green. 

 Hah. Schuylkill River, United States {Br. J. Leidy). 

 Examined in the dried state. 



I am indebted to my friend Prof. Leidy of Philadelphia for a spe- 

 cimen of this species, 3| inches long, 2|^ inches wide, and ith of an 

 inch in thickness. The whole of the upper surface is thickly and 

 rather uniformly studded with variously shaped elevations, none of 

 which exceed about a line in height ; and each one has on its summit 

 one or more oscula, and frequently as many as five or six, the whole 

 being enclosed within a slightly raised, thin margin. The oscula are 

 exceedingly numerous, but very minute. The pores are readily to be 

 distinguished by the aid of a lens of 2 inches focus. The whole sur- 

 face of the sponge is minutely hispid from the projection of the ter- 

 minal spicula of the primary lines of the skeleton-tissue. 



The spicula of the skeleton are short and stout ; an average-sized 

 one measured yi-^ inch in length, and had a diameter of -goVff inch. 

 I could not detect any tension-spicula in either the dermal or inter- 

 stitial membranes. 



The ovaria are rather abundant at the basal surface of the sponge; 

 they are very small, and are scarcely visible to the unassisted eye. 

 In the dried state they are nearly all of them more or less hemisphe- 

 rical by contraction, but their normal form is spherical. In the 

 adult state they are furnished with a closely packed stratum of biro- 

 tulate spicula. They are very minute, an adult one measuring 

 -^;xTa ^^^ in length, the diameter of the rotulse being ygVo inch, 

 and the diameter of the shaft yg-^oo inch. They are not visible, ex- 

 cepting by previous preparation in boiling nitric acid. The margins 

 of the rotulse are very entire, and in fully developed spicula that of 

 the outer one is frequently exflected ; but I did not observe this cha- 

 racter to occur in any of the proximal ones. In a very few instances 

 the shaft of the spiculum was continued through the centre of the 

 distal rotula, forming an acutely terminated central spike. 



When a section at right angles to the dermal surface of the sponge 

 was examined, two distinct layers of growth were visible, the first 

 dermal membrane remaining in the midst of the sponge. From this 

 circumstance it appears probable that the species is perennial, and, 

 from the last stratum being in perfect accordance with the first, that 

 its natural character is that of a thin coating sponge, never rising in 

 the form of tuberous masses like the closely allied European species, 

 S.fluviatilis. 



The specific names friabilis and fragilis have been applied so 

 loosely and indefinitely to the European species that I do not think 

 it advisable to adopt the latter, which was appended to the specimen 



