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 CoUineUa inscrijjta (Fig. 534:), of which 

 the fossil precursor may have been Trachysycon. Resembling 

 Sidcastrella clcmsa (Fig. 535), dredged off Sand Key in 129 



Fig. 534. — Collinella iiiscripta. f . Fig. .535. — Sulcastrella clausa. |. 



fathoms, are a number of cretaceous sponges to which Zittel 

 has given the name of Astrobolia. 



Cup-shaped sjDonges having bunches of spicules scattered over 

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



Fig. 536. — Setidium obteetum. |. 



Lithistidfe. An interesting lithistid is a small form, TremauU- 

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

 an inward tubular extension of the cuticle. 



:m.^ni'i 



<. .f -.r 



.*:1 

 ■f^- 



Fig. 537. — Tremaiilidium geminiim. \. 



