303 







PLATE LXXXVII. 



HTMEDESMIA INDISTINCTA, Bowerbank. 



Fig. 1. Represents the fragment of a bivalve shell 

 nearly covered by the thin coating of the sponge. 

 Natural size. 



Fig. 2. A small piece of the sponge mounted in 

 Canada balsam. X 150 linear. 



Fig. 3. One of the long, slender, acerate tension 

 spicula from the dermal membrane. X 250 linear. 



Fig. 4. A bidentate, equi-anchorate, retentive 

 spiculum from the dermal membrane. X 530 linear. 



Fig. 5. One of the dentato-palmate equi-anchorate 

 retentive spicula from the dermal membrane. X 530 

 linear. 



Fig. 6. One of the long, slender, attenuato-acuate 

 skeleton spicula. X 150 linear. 



Fig. 7. The basal portion of one of the skeleton 

 spicula. X 250 linear. Exhibiting the mode of its 

 basal spination, 



Fig. 8. One of the cylindrical entirely spined ten- 

 sion spicula of the basal membrane. X 250 linear. 

 These spicula are frequently of unequal diameter. 



Figs. 9 and 10. Two of the acuate, entirely, but 

 incipiently, spined internal defensive spicula from the 

 basal membrane. X 250 linear. 



IsoDiCTYA OBSOUEA, Bowefbanjc. 



Fig. 11. Represents the best and most satisfactory 

 specimen of the species that I have yet seen. 



In the type-specimen of this species, represented in 

 Plate LXXYI, a small portion of the species only is 



