CHARACTERISTIC DEEP-SEA TYPES. SPONGES. 



175 



beautiful specimens collected oft' Frederichstaed in 180 to 208 

 fathoms, in thick globigerina ooze. A fine Holtenia Pourta- 

 lesi'i (Figs. 531, 531 a, 531 b, 531 c) was collected by Pourtales 

 off Sand Key, in depths varying from 184 to 324 fathoms. 



The group of Lithistidse, as defined by Zittel, includes 

 sponges, formerly united with the Hexactinellidse, characterized 



Fig. 532. Vetulina stalactites. Greatly magnified. (Schmidt.) 



by their connected calcareous spicules (Fig. 532), not built upon 

 the three-axis type, but forming an apparently irregular maze. 



The majority of the specimens of Vetulina stalactites (Fig. 

 533) are thick, undulating sheets, closely perforated with irreg- 



iff. 533. Vetulina stalactites, f . 



ularly placed pores. The arrangement of the calcareous skele- 

 ton recalls to a certain extent that of the Hexactinellidse. The 



