176 



THREE CRUISES OF THE " BLAKE.' 



genus Vetulina was previously known only from the Jura ; it 

 was quite commonly dredged off Barbados in 100 fathoms. An 

 allied sponge, from 292 fathoms off Morro Light, Havana, is 

 the little pear-shaped Collinella inscripta (Fig. 534), of which 

 the fossil precursor may have been Trachysycon. Resembling 

 Sulcastrella clausa (Fig. 535), dredged off Sand Key in 129 



Fig. 534. Collinella inscripta. |. Fig. 535. Sulcastrella clausa. . 



fathoms, are a number of cretaceous sponges to which Zittel 

 has given the name of Astrobolia. 



Cup-shaped sponges having bunches of spicules scattered over 

 the surface, like Setidium (Fig. 536), are unusual among the 



Fig. 536. Setidium obtectum. ^. 



Lithistidae. An interesting lithistid is a small form, Tremaull- 

 dium geminum (Fig. 537), in which the pores are replaced by 

 an inward tubular extension of the cuticle. 



Fig. 537. Tremaulidium geniinnnfe ^- 



