18/3.] DR. J. S. BOWERBANK ON THE SPONGIADJE. 1" 



The pitting or areolation of the surface of the sponge is scarcely 

 seen by the unassisted eye ; with the aid of a two-inch lens it very 

 closely resembles the pock-marks on the human face. The dis- 

 position of the large sphero-stellate spicula in the dermal rind is 

 different from those in any other nearly allied species. Instead of 

 being evenly distributed throughout its substance, they are collected 

 into two dense strata at the outer and inner surfaces of that organ, 

 while the intervening space has comparatively a few only distri- 

 buted in its substance, and in these comparatively clear spaces 

 the smaller description of subsphero-stellate retentive spicula are 

 abundant. The large sphero-stellate spicula very closely resemble 

 those of Tethea robust a and T. Ingalli ; but they are less robust in 

 form than those of the former, and more so than those of the latter 

 species. The greatest diameter of one of the largest size was - 4 -^ r 

 inch. 



The minute subsphero-stellate retentive spicula with clavated cy- 

 lindrical radii are exceedingly various in both size and form. In 

 some the radii are slender with very slightly developed bulbous ter- 

 minations, while others, with the radii quite as slender, have large 

 well-developed distal terminations ; and in some the radii are short 

 and stout with a very slightly developed bulb. These minute organs 

 are strikingly different in form from the corresponding ones in any 

 of the nearly allied species, and are certainly the most distinctive of 

 all the specific characters of the species. The average size of the 

 greatest number is tbW * u{m extreme diameter ; but there were a few 

 that measured -gi-y inch iu diameter. They require a power of about 

 700 linear to distinctly demonstrate their forms ; one of the smallest 

 did not exceed g^rff inch in extreme diameter. 



The skeleton-spicula vary to a considerable extent in size and in 

 the degree of their fusiformity, so as in some almost to simulate the 

 acerate form. The really acerate and cylindrical ones are of very 

 rare occurrence. 



The sarcode in all parts of the sponge appears to be very dense. 



It is most likely that succeeding specimens of this species may 

 not exhibit any of the extraordinary basal appendages that render 

 the specimen figured so singular in its appearance. Such organs 

 appear to be only thrown out when a necessity for them arises from 

 the peculiarities of the locality impeding the safe attachment of the 

 young sponge. Similar appendages are projected from the bases of 

 Tethea norvagica ; and there is little doubt that such organs will be 

 observed to be thrown out by other species of Tethea when a neces- 

 sity for them arises. 



Leuconia GLOMER03A, Bowerbank. (Plate IV.) 

 Sponge sessile? composed of a closely compressed mass of repeat- 

 edly divaricating, slender, compressed, ascending branches. Surface 

 smooth. Cloacae continuous from base to apex of the branch through 

 all its divarications ; terminal orifice rarely ciliated ; oscular surface 

 coarsely reticulated ; rete multispiculous. Oscula large and open. 

 Pores inconspicuous. Dermis — dermal membrane thin, spiculous ; 

 Proc. Zool. Soc— 18/3, No. II. 2 



