58 A MONOGRAPH OF THE 



spaces liumerous and small ; the acerate retentive spicula are 

 few in number, the abundance of the skeleton ones ren- 

 dering their presence to a great extent unnecessary, and 

 a few doliolate cylindrical spicula were disposed on the 

 membranes. On some portion of the membranes the 

 elongo-stellate spicula were thinly dispersed, but in many 

 parts they were entirely absent. 



Genus — Polymastia, Bowerbank. 



Section * * Skeleton spicula, acuate. 



1. Polymastia ornata, Bowerbank. 



2. — bullosa, Bowerbank. 



3. — robusta, Bowerbank. 



4. — brevis, Bowerbank. 



5. — spinula, Bowerbank. 



6. — radiosa, Bowerbank. 



Section * * * Skeleton spicula, spinulate. 



7. Polymastia mammillaris, Bowerbank. 



1. Polymastia obnata, Bowerbank. 



Sponge. Sessile (?). Base unknown ; fistula single, large, 

 and long. Surface abundantly but minutely hispid. 

 Oscula congregated at the distal extremity. Pores 

 inconspicuous. Dermal membrane pellucid, rather 

 stout, abundantly furnished with short and stout 

 acuate spicula, based on the external surface of the 

 membranes ; irregularly depressed, radiating in every 

 direction. Skeleton : primary lines constructed of 

 continuous large, compact, parallel, cylindrical fasci- 

 culi of spicula, dispersed at regular intervals, and 

 extending from the base to the apex of the fistula, in 

 a slightly spiral direction. Secondary or interstitial 



