4r>2 



THE VOYAGE OF H.M.S. CHALLENGER. 



of the collection is concluded; so far I will content myself with stating that the majority 

 of the Tetractinellid Sponges are not usually inhabitants of very deep water, they rather 

 affect shallow water, say from 10 to 50 fathoms, but occasionally extend to greater depths, 

 such as 1000 fathoms. There is only one characteristic exception to the rule, viz., in the 

 case of the genus Thenea, which is usually found at depths of from 1000 to 1800 fathoms, 

 but sometimes enters shallower water ; in one case it was obtained from the compara 

 tively shallow depth of 95 fathoms. 



" Tetractinellid genera appear to be of world-wide distribution, but certain subgeneric 

 groups of species appear to be restricted to particular areas. Thus, such a group as the 

 Stellettina, characterised by a particular form of minute spicule, occurs along the track 

 of the Challenger at various points between Australia and Japan. Another group appears 

 to be confined to Southern Australia. 



" Although I expect to add much on distributional questions when I have completed 

 my study of the collection, I consider that the chief additions to our knowledge will be 

 found to bear on problems of histology and minute anatomy." 



