241 



PLATE LXXVIII. 



ISODICTYA INGALLI, Bowerb.cmk. 



Fig. 1 . Represents one of the most characteristic 

 of the three specimens in my possession. Natural size. 



Fig. 2. A fully-developed skeleton spiculum. X 

 250 linear. 



Fig. 3. A young and slender spiculum. x 250 

 linear. 



Every degree of tenuity may be seen between this 

 spiculum and the one represented by fig. 2, but the 

 latter prevails greatly in number. 



Fig. 4. Represents a small piece of the dermal 

 membrane of I. Ingalli. X 123 linear. 



Fig. 5. A small piece of the dermal membrane of I. 

 simulans. X 123 linear. Exhibiting the essential dif- 

 ferences in the two structures. 



DESMACIDON COLUMELLA, Bowerbanlc. 



Fig. 6. Represents the type-specimen from the 

 cabinet of Mr. Edward Parfitt. Natural size. 



Fig. 7. One of the fusiformi-cylindrical skeleton 

 spicula. X 250 linear. 



Fig. 8. Two of the gernmules in situ on a portion of 

 the interstitial membranes. X 530 linear. 



ISODICTYA INGALLI, Boiverbank. 

 Plate LXXVIII. 



Sponge. Branching irregularly, hard and rigid in the 

 dried state. Surface smooth. Oscula simple, slightly 



16 



