332 DR. J. S. BOWERBANK ON THE SPONG1AD.E. [Mar. 18, 



Fig. 4. An end view of one of the dentato-cylindro-hexradiate spicula, magnified 

 530 linear. 



5. A malformed specimen of the dentato-cylindro-hexradiate form of spi- 



culum, magnified 530 linear. Malformations of this spiculum are 

 not uncommon. 



6. An average-sized acuate skeleton-spiculum, magnified 80 linear. 



7. One of the spicula from the interstitial membranes, magnified 80 linear. 



Plate XXX. 



Ecionemia acervus, Bowerbank. 



Fig. 1 represents a fully developed fusiformi-acerate skeleton-spiculum. magni- 

 fied 80 linear. These spicula vary to a very considerable extent in size. 



2. A full-sized attenuato-expando-ternate connecting-spiculum, magnified 



80 linear, 



3. A fully developed attenuato-recurvo-ternate connecting-spiculum, mag- 



80 linear. 



4. Two of the subtuberculated fusiformi-cylindrical tension-spicula from 



the dermal membrane, magnified 530 linear. 



5. One of the subsphero-attenuato-stellate retentive spicula, magnified 



530 linear. 



6. A minute cylindro-sphero-stellate retentive spiculum from the inter- 



stitial membranes, magnified 530 linear. 

 By an accidental omission, one of the minute and slender acerate tension and 

 external defensive spicula was not figured as intended. Those spicula are 

 identical in form with the one represented by fig. 10 in the present Plate, from 

 Ecionemia densa, the only difference being that those of E. acervus are much 

 less in both length and diameter. 



Ecionemia densa, Bowerbank. 



Fig. 7 represents one of the fusiformi-cylindrical skeleton-spicula, magnified 

 80 linear. 



8. One of the attenuato-expando-ternate connecting-spicida, magnified 80 



linear. 



9. A portion of a larger specimen of an attenuato-expando-ternate connect- 



ing-spiculum, the radii of which are cylindrical, magnified 80 linear. 



10. One of the small and slender acerate tension-spicula, from the intersti- 



tial membranes, magnified 80 linear. 



11. Two of the tuberculated subcylindrical tension-spicula from the inter- 



stitial membranes, magnified 530 linear. 



12. An attenuato-steUate entirely spined retentive spiculum, magnified 530 



linear. 



13. One of the cylindro-sphero-stellate entirely spined retentive spicula, 



magnified 530 linear. 



14. A cylindro-sphero-stellate retentive spiculum, radii spineless, magnified 



530 linear. 



Bictyocylindrus sctosus, Bowerbank. 

 Fig. 15 represents a portion of a terminal group of setse, from the distal end 

 of the sponge, with a small piece of the dermal membrane and its 

 characteristic spicula, magnified 80 linear. 



16. One of the flexuous cylindrical skeleton-spicula from the axis of the 



sponge, magnified 150 linear. 



17. An acerate spiculum from one of the setoe, magnified 150 linear. 



Plate XXXI. 



Pachymatisma inconspicua, Bowerbank. 



Fig. 1. One of the subfusiformi-acerate skeleton-spicula, magnified SO linear. 

 2. An average-sized superexpando-t ornate attenuated connecting-spiculum, 

 magnified 80 linear. These spicula vary greatly in their size and 



