Sollas — On Tetractinellid Sponges. 179 



0"039 mm. ; (3) calthrops, usually quadriradiate, but frequently 

 tri- and bi-radiate, or sometimes quinqui- and sex-radiate ; one 

 ray of a tetrad, 0'0276 by 0-004 mm.; (4) stellates : these differ 

 from the calthrops by possessing more numerous and smaller raj^s. 

 Habitat— Station 192, lat. 5° 49' 15" S.; 132° 14' 15" E. ; 

 140 fms. 



Family 3. CORTICID^. 



Genus 1. Thrombus, g. n. — Corticidse, containing spined forks 

 like those of Corticiam kittoni, Carter {Thrombus kittoni), see Ann. 

 Mag. Nat. Hist., ser. 4, vol. xiv., p. 24. 1874. 



Thrombus challengeri, sp. n. — Mesoderm, a collenchyme which 

 contains numerous oval granular cells, 0-016 to 0*02 mm. in 

 diameter. Spicules like those of Thrombus kittoni, but larger ; 

 fork, shaft, 01 by 0-012 mm. ; arms, 0-055 by 0-012 mm. 



Habitat— Station 177; lat. 16° 45' S. ; long. 168° 7' W. ; off 

 Api, New Hebrides, 130 fms. 



Sub-order 2. 

 Family 1. TETILLIDiE. 



Genus 1. Tetilla, O. Schmidt. — The ectosome never forms a 

 cortex, and is not provided with special spicules ; the mesoderm, 

 is a collenchyme, and the canal system eurypylous. > 



Tetilla sandalina, sp. n. — Sponge small ; more or less ellipsoidal,, 

 or fusiform ; a single lateral oscule at one end ; ectosome not deve- 

 loped ; flagellated chambers large. Spicules — (1) fusiform acerate, 

 2'326 by 0-0237 mm. ; (2) trichite acerates, - 395 mm. long ; 

 immeasurably thin ; (3) trifid forks with filiform proximal ends ; 

 arms of unequal length ; one about 0-197, the other two 0-0513 mm. 

 long ; (4) arculi and sigmellse about 0-025 mm. long ; anchors 

 absent. 



Habitat— Azores, lat. 37° 26' N. ; long. 55° 13' W. 1000 fms. 



Tetilla leptoderma, sp. n. — Sponge small; somewhat spherical; 

 a single oscule, lower surface produced into slender rootlets, 

 ectosome thin ; flagellated chambers large. Spicules — (1) a fusi- 

 form acerate, 4*185 by 0-0474 mm. ; (2) trifid forks, filiform at 

 one end, rays of unequal length at the other, 4-03 by 0'0118mm. ; 



2 2 



