ISODICTTA. 127 



from the dermal surface mounted in Canada balsam 

 ■was submitted to microscopical examination with a 

 power of 100 linear, the dermal reticulation presented 

 a very beautiful appearance; although very irregular in 

 its structure it forms a strikingly distinct specific 

 character. 



" The areas of the network are not more than about 

 half the length of a spiculum wide, and by far the 

 greater number of them are triangular ; and the rete 

 bounding the areas varies considerably in its structure, 

 from being multispiculous to a single spiculum. The 

 pores were in an open condition ; they were dispersed 

 among the areas, there being rarely more than one in 

 each of them. 



" The skeleton is very diffusely constructed and 

 exceedingly irregular, and it is only near the dermal 

 surface that the true Isodictyal character can be 

 recognised with certainty. The interstitial cavities 

 are large and numerous, thus producing a great compli- 

 cation of its structures. The primary lines of the 

 skeleton vary considerably in their structure, the 

 spicula being very numerous in some, while they are 

 very few in others. The same structural irregularity 

 obtains in the secondary lines of the skeleton, and the 

 irregularity of their disposition adds to the confusion. 

 Amidst all this structural complication the skeleton is 

 unmistakably that of an Isodictya. 



" There is but one form and size of the spicula in this 

 sponge, the subfusiformi-acerate. A fully developed 

 skeleton one measured -j-g-jg- inch in length and -g-ooo 

 inch in diameter. These dimensions are greatly in 

 excess of those of the spicula of the greater number 

 of species of Isodictya in this division of the genus. 



