303 



PLATE LXXXVII. 



Hymedesmia indistinota, Boiverbanh. 



Kg. 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 260 linear. 



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

 spiculum from the dermal membrane. X 530 linear. 



Fig. 5. — One of the dentato-pahnate 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 cyhndrical 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 OBSCUKA, Boioevbank. 



Fig. 11. — Represents the best and most satisfactory 

 specimen of the species that I have yet seen. 



In the type-spechnen of this species, represented in 

 Plate LXXVI, a small portion of the species only is 



