96 A MONOGRAPH OF THE 



fusiform in their proportions. The skeleton spicula are 

 comparatively long and large, and slightly fusiform, and 

 the form of their spinulation is very peculiar, the bulbous 

 base being oviform, the distal portion being the smallest. 

 This character appears to be a very constant one, and 

 appertains to the dermal defensive spicula as well as to the 

 skeleton ones. 



The large tension spicula strengthen and support the 

 interstitial tissue most effectively ; they cross the skeleton 

 fasciculi and each other in every possible direction, and are 

 very numerous. The smaller description of tension spicula 

 are very slender and delicate in their proportions, and are 

 closely packed together in a fasciculus that rarely exceeds 

 the length of one of the spicula. The fasciculi are irregu- 

 larly dispersed on the interstitial membranes ; two or three 

 fasciculi are occasionally found together. 



Genus — Halicnemia, Bowerbank. 



1. Halicnemia patera, Bowerbank. 



Sponge. Circular, concavo-convex, very thin ; sessile, 

 radiating from a small pebble imbedded in its centre. 

 Upper surface convex, hispid by the projection of nu- 

 merous bundles of long, slender, acerate defensive spi- 

 cula ; fasciculi radiating from the centre to the sur- 

 face, and to the circumference, where they form a deep 

 marginal fringe. Lower surface concave, smooth, and 

 even. Oscula simple, dispersed on the lower surface, 

 numerous and minute. Pores inconspicuous. Der- 

 mal membranes pellucid, spiculous; spicula very 

 numerous, dispersed, fusiformi-acerate, entirely spined, 

 subangulated, and frequently inflated at the middle. 

 Skeleton. Spicula, attenuato-spinulate and fusiformi- 

 spinulate, short and stout ; and spiuulate long and 



