442 Prof. W. J. Sollas on the 



dried one, so that the results are not trustworthy. The cal- 



cuhition is as follows : — Total area 6*16 square inches, total 



poral area consequently 0*59136 square inch ; area of single 



P 0-59136 

 oscule 0*0416 square inch : rr= ,, ," ,,. =14'2. The small- 

 ^ ' O 0-041b 



ness of this number is probably due to the large size of the 



oscule, consequent on its enlargement by drying. 



To ascertain, further, whether any definite relation exists 

 between the general and oscular areas, and consequently be- 

 tween the poral and oscular areas, the largest of Mr. Norman's 

 specimens was examined. In form it approximates to a 

 hemisphere with a radius of 1*4 * so that its total area may be 

 taken as 1 8*475 square inches. It bears six oscules, giving 

 one to every 3*08 square inches of total area. 



In the first examined specimen (see antea) we had 2*26 

 square inches to one small oscule, in the second 6*16 square 

 inches to one large oscule ; taking an average from these we 

 have 4*21 square inches to each oscule. Though this is 

 sufficiently greater than the value found from the third speci- 

 men to prove that the relation between the general and oscular 

 ai-ea is by no means precise, it yet indicates some kind of 

 broad connexion which it may be worth while to further 

 investigate. 



The Skeleton. — The large spicules of the skeleton are stout 

 fusiform, and slender filiform, acerates, simple and bifurcated 

 forks, and variously-shaped grapnels. The small spicules are 

 spinispirula3 of two kinds : — (i.) The stout fusiform sharp- 

 pointed acerates are the staple body-spicules 5 they measure 

 frequently 0*2 inch in length by 0*034 in breadth, and 

 appear sometimes to attain to as much as 0*5 inch in length. 

 (ii.) The long slender acerates, which project beyond the 

 general surface of the sponge, are seldom seen entire, so 

 that it remains doubtful in many cases whether they are truly 

 acerates or only the shafts of grapnel-spicules ; they may 

 reach 0*7 to 0*8 inch in length, (iii.) The commonest forks 

 (Kent (vii.), figs. 6, 7) are bifurcated ternates with exceedingly 

 long rays, the primary rays usually measuring about O'OJ 

 inch, and the secondary 0*047 inch in length ; the shaft varies 

 greatly, but is often 0*19 to 0*2 inch long ; at a short distance 

 below the head it often undergoes a rapid diminution in thick- 

 ness, becoming almost filiform towards its proximal end, 

 something like a tap-root, (iv.) The forks {vide Bwk. (x.), 

 fig. 3) with undivided simple rays are frequent ; they are also 

 of very various sizes, 27 inch is a not unusual length for the 

 shaft, and 0*034 inch for the rays. 



it is not unusual for bjth kinds of forks to have the rays 



