368 A MONOGRAPH OF THE 



considerably elevated, or they are large and terminal orifices 

 at the distal parts of the sponge. 



The dermal reticulation is very irregular, but it appears 

 to be always unispiculous, and the sides are composed each 

 of a single spiculum. Each area contains two or three 

 minute pores. The dermal spicula are of the same form as 

 those of the skeleton, but a little less stout. 



The skeleton is very unequal in the extent of its deve- 

 lopment at different parts of the sponge ; in the older 

 portions the fibres are well produced, and the primary ones 

 multispiculous, while in the younger parts the general aspect 

 of the skeleton is very much like that of an Isodictya, and the 

 primary fibres are scarcely distinguishable in their structures 

 from the secondary ones. 



The spicida are regularly acerate, and are short and stout ; 

 one of the largest measured ^th inch in length, and gg^th 

 inch in diameter. 



The interstitial membranes do not appear to exist to an 

 equal extent in all parts of the sponges, but to occur irre- 

 gularly in detached patches ; some of these spots are 

 abundantly furnished with tension spicula of about the 

 same length as those of the skeleton, but much more 

 slender ; in other parts there are very few of them present. 



Dr. Johnston, in his ' History of British Sponges,' page 

 101, describes, without figuring, Halichondria Columbce in 

 the following terms: "Irregularly latticed by rounded 

 inosculating branches ; spicula double pointed and curved." 

 This meager description will apply equally well to Chalina 

 Montaguii and Flemingii, and to Isodictya simulans in its 

 fullest state of development, and I feel strongly persuaded 

 to conclude that the sponges described by Dr. Walker in 

 his essays, page 196, as Sjmngia Columba;, and that by 

 Sowerby, ' British Miscellany,' page 131, and plate 60, as 

 Spongia canccllata, are, in fact, but specimens of Chalina 

 Montaguii; and I am led to this conclusion by the fact 

 that among the very large number of specimens of Chalina 

 Montaguii examined, I have been quite unable to find any 

 one that possessed such organic distinctive characters as 

 would entitle it to be considered as at all likely to be a 



