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. 



Sulcastrella clausa. I. 



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. %■ 



Lithistidse. An interesting lithistid is a small form, Tremcmli- 

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

 an inward tubular extension of the cuticle. 



Fig. 537. — Tremaulidium geminum. \- 



