No. v.— REPORT ON THE HEXACTINELLID SPONGES (TRIAXONIDA) 

 COLLECTED BY H.M.S. "SEALARK" IN THE INDIAN OCEAN. 



By Arthur Dendy, D.Sc, F.R.S., F.L.S., Professor of Zoology in the 

 University of London {King's College). 



(Plates 40—43.) 

 Read 17th June, 1915. 



The " Sealark " collection contains only three species of Hexactinellid Sponges, but 

 these are all extremely interesting forms, and I venture to hope that the somewhat 

 detailed study that I have been able to make of them may add materially to our 

 knowledge of this remarkable group. 



Aulocalyx serialis is a new species of a genus hitherto known only by fragments of the 

 type species [A. irregularis) obtamed by the "Challenger" expedition and described by 

 Schulze. 



Heterorete pulchra is the type species of a new genus related to Dactylocalyx, and 

 remarkable for the entire absence of special dermal and subdermal spicules. Fortunately 

 the material of this species was much better preserved than is usually the case with 

 hexactinellids, so that I am able to give some particulars as to the soft tissues and canal 

 system. This sponge is further interesting on account of the presence in it of a commensal 

 or parasitic hydroid ramifying through the substance of the wall, as well as of numerous 

 Anthozoa attached to the surface. 



Sarostegia oculata is a very beautiful and remarkable sponge, first described by 

 Topsent from deep water off the Cape Verde Islands. 



The preparation of this Report has been greatly facilitated by a grant from the 

 Trustees of the Percy Sladen Memorial Fund to enable me to pay an assistant. I desire 

 to express my thanks to the Trustees for their generous action, and I wish also to express 

 my indebtedness to Miss Hilda Lucy Deakin, the assistant appointed, by whom most of 

 the microscopical preparations and drawings of skeletal structures have been made, for 

 the skill and care with which she has carried out the work entrusted to her. 



The drawing's of external forms were made for me by Mr T. P. Ceilings. 



Genus Aulocalvx Schulze [1887]. 



This genus was founded by F. E. Schulze in 1887 for the reception of several 

 fragmentary specimens obtained by H.M.S. "Challenger" from a depth of 310 fathoms 

 off Marion Island, south-east of the Cape of Good Hope, and between Marion Is. and the 

 Crozets at a depth of 1600 fathoms, and thus practically within the area of the Indian 



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