ARTICLE II. ON THE STRUCTURE OP CERATELLA FUSCA (GRAY), BY W. BALDWIN 

 SPENCER, M.A., PROFESSOR OF BIOLOGY IN THE UNIVERSITY OF MELBOURNE. 

 (With Plates 2, 3, and 3a.) 



(Read Thursday, June llth, 1891.) 



I have to thank Dr. Ramsay and the Trustees of the Australian Museum, 

 Sydney, for the opportunity of examining the structure of this interesting hydroid 

 form. The specimens examined came from Bondi on the New South Wales coast 

 and from Lord Howe Island, where they were collected by Mr. Whitelegge of the 

 Australian Museum, whom I have to thank for kind assistance. The Lord Howe 

 Island specimen had the zooids beautifully expanded. 



Dr. Gray* was the first to describe and figure Ceratella and the closely allied 

 genus Dehitella from specimens in the British Museum. He had dried specimens 

 only at his disposal and his description necessarily refers only to the hard parts 

 and these having the form of a horny network somewhat resembling in general 

 appearance the skeleton of a horny sponge, led him to place the two forms 

 provisionally amongst the sponges. For their reception he constituted the family 

 Ceratelladcz. Five years later Mr. H. J. Carterf published a paper entitled 

 " Transformation of an Entire Shell into Chitinous Structure by the Polype 

 Hydractinia, with short Descriptions of the Polypodoms of five other Species." In 

 this he refers to Ceratella fusca and Dehitella atrorubeus and describes two new forms 

 belonging to the former genus under the names of C. procumbens and C. spinosa. 

 Both of these came from South Africa the former from the Cape of Good Hope and Natal 

 the latter from Natal. In the same paper he describes a new genus Chitina with a 

 single species C. ericopsis which came from New Zealand. Reference to these will 

 again be made after the anatomy of Ceratella fusca has been described, meanwhile 

 it is sufficient to note that Mr. Carter's investigations of a species of Hydractinia 

 (H. levispina) with a skeleton composed of a horny network which incrusts and eats 

 its way into univalve shells led him to re-examine the two forms placed by Dr. Gray 

 in the family Ceratelladae and in consequence of his finding undoubted traces of 

 thread-cells in the dried specimens both of these and of the two new species 

 of Ceratella mentioned above, he rightly recognised them as belonging to the 



* Proo. Zool. Soc., Nov., 1868. 



t An. and Mag. Nat. Hist., Jan., 1873. 



