6 DR. 3. S. BOWERBANK ON THE SPONGIADjE. [Jan. 7, 



protecting the dermal membrane from its minute enemies. These 

 spicula are in strong contrast with the primary series of external 

 defensive ones, which equal those of the skeleton in length and dia- 

 meter. They are frequently g of an inch in length, with a diame- 

 ter of it^t; inch, while those of the long and slender secondary series 

 are from tV to tr mcn m l eu g tn > &n & do Dot exceed ^Vo i ncn m 

 diameter. 



The sponge has evidently suffered from partial decomposition, 

 and I could not find any portion of the dermal membrane remain- 

 ing in a condition for satisfactory examination ; but if we may judge 

 by the profusion of the spicula in the other membranes of the 

 sponge, it will probably prove to be abundantly spiculous. 



The skeleton-fasciculi are large and strong, and especially so 

 near the dermal surface, where strong shafts of the patento-ternate 

 connecting spicula are iocorporated with them. The latter form are 

 very numerous and much larger and stouter than those in many 

 other species of the genus. Their length frequently exceeds £ inch, 

 their greatest diameter is -^^ inch, and the expansion of their ternate 

 radii varies from -^ to jf- {T inch. The average dimensions of the 

 skeleton- spicula is, length g inch, and greatest diameter ^j-- inch. 



The recurvo-ternate spicula are also more than usually large 

 and numerous ; their slender shafts are frequently 5 inch in length, 

 while their greatest diameter does not exceed 2 ' inch. 



The interstitial membranes are in a fine state of preservation, 

 and are coated abundantly with sarcode ; and in many parts they 

 are literally crowded with the two forms of stellate retentive spicula, 

 each form being about equally abundant ; on some parts of the 

 membranes they are so numerous as to render it impossible to dis- 

 criminate their forms. 



There is another, a larger specimen of G. depressa in the Museum 

 of the Royal College of Surgeons. In its general anatomical de- 

 tails it is in perfect accordance with the one described. In the 

 larger specimen, on what was probably the upperside of the sponge, 

 rather on one side near the thickest portion, there is an elliptical 

 orifice five eighths of an inch long by a quarter of an inch wide, lead- 

 ing into an expanded cavity one and a half inch deep, in which most 

 probably the oscula are congregated, as we find them to be in many 

 other species of the genus. On the distal end of the sponge thelittle 

 depressions on its surface indicating the intermarginal cavities beneath 

 are in a good state of preservation ; and it is probable, from their 

 forms and modes of disposition, that the pores in this species are 

 congregated. 



Geodia gibberosa, Lamarck. (Plate I.) 



Sponge massive, sessile ; surface more or less tuberculated. Der- 

 mal membrane thin, pellucid ? Connecting spicula attenuato-pa- 

 tenti-ternate, slender. Oscula small, congregated in depressed 

 areas in mature specimens ; loosely congregated or dispersed in 

 young specimens. Pores inconspicuous. Skeleton-spicula fusi- 

 formi-acerate, slender, and, rarelv, acuate slender. Interstitial 



