28 DR. J. S. BOWERBANK ON CEYLONESE SPONGES. [Jan. 7, 



Where the true fibre prevails, and the increment of the skeleton 

 is progressing, a single thread may be seen projected from the outer 

 surface of a grain of sand, to some distance, without having met 

 with a grain to which it could attach itself, and at its distal extremity 

 there will be seen a single large or small molecule of sand elevated, 

 as it were, on a pedestal, or an irregular cup-shaped membrane 

 which has only partially enveloped a particle and then lost it ; or a 

 column of large and small grains will be seen projected from the 

 mass, the distal grain of which always exhibits more or less exten- 

 sions of keratose tissue in search of additional grains of sand to be 

 incorporated in the fibrous skeleton of the sponge. 



The dermal membrane is thin and pellucid ; it is covered with a 

 single stratum of grains of sand and a few foraminated shells ; in the 

 interstices of these grains a few open pores were visible. 



The oscula are variable in size ; ten or twelve were dispersed over 

 the surface of the sponge ; the largest rather exceeded a line in dia- 

 meter. 



Isodictya Donnani, Bowerbank. (Plate VI.) 



Sponge cup-shaped, parietes thick and strong ; margin strongly 

 undulated, distal edge finely plicated, surface externally and intern- 

 ally even, minutely hispid. Oscula and pores inconspicuous. Dermal 

 membrane abundantly spiculous ; spicules the same as those of the 

 skeleton, and very small and slender acuate ones, dispersed. Skele- 

 ton — primary lines multispiculous, strongly developed, rather irre- 

 gular ; secondary lines very irregular, varying from multispiculous 

 to unispiculous, very numerous ; spicula acuate, short and stout. 

 Interstitial membranes abundantly spiculous ; tension-spicula acuate, 

 small and slender, dispersed, rather numerous. Sarcode dark amber- 

 colour. 



Colour, alive, bright orange ; dark purple in the dried state. 

 Sab. Pearl-banks, Ceylon (Mr. Holdsivorth). 

 Examined in the dried state. 



I have named this species after Capt. Donuan, the present Super- 

 intendent of the Pearl-banks. 



I received a single specimen of this interesting sponge from Mr. 

 Holdsworth for examination. The parietes of the cup are remarkably 

 firm and thick ; and at about half its height from the distal end of 

 the short pedicle the undulation of the marginal portion of the cup 

 commences, and increases to such an extent as to occupy at least 

 two thirds of its entire diameter. The extreme edge of the cup is 

 thick and rounded, and is plicated in such a manner as to closely 

 resemble the distal end of a lady's fan when in a closed condition. The 

 short basal column does not exceed half an inch in height in its pre- 

 sent condition. It has every appearance of having been broken 

 from its natural attachment while in a living state. 



The surface of the outer and inner portions of the cup are even, 

 but not smooth to the touch, from the projection of the terminations 

 of the primary lines of the skeleton. The hispidation is visible only 



