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XIV. The Croonian Lecture. — On the Structure of the Stylasteridae, a Family of 
the Hydroid Stony Corals. 
By H. N. Moseley, F.R.S., Fellow of Exeter College, Oxford , late Naturalist on hoard 
H.M.S. £ Challenger .’ 
( Published by permission of the Lords Commissioners of the Treasury.) 
Received January 22, — Read February 28, 1878. 
[Plates 34-44.] 
INTRODUCTION. 
In the Proceedings of the Royal Society, No. 172, 1876, I published a preliminary 
note on the present subject, and gave a short account of the results which I had 
arrived at from a somewhat hurried examination of the material at disposal. After 
this short account had been written, I devoted my time during the remainder of the 
homeward voyage of PI.M.S. ‘ Challenger ’ 'to the further study of the structure of the 
Stylasteridae, and the preparation of drawings illustrating it. I have supplemented 
this work by additional work in England, and the results are embodied in the present 
paper. The main part of the specimens of Stylasteridae, from the study of which the 
anatomical details were determined, was obtained at a single haul of the trawl-net 
taken on February 14th, 1876, in lat. 37° 17 ' S., long. 53° 52' W., off the mouth of 
the Rio de la Plata in a depth of 600 fathoms. The specimens then obtained included 
six genera of the family of the Stylasteridae. They were in most excellent preserva- 
tion, although they had been slowly raised from the bottom, and in all the genera but 
one the generative organs were in full development. It was the examination of this 
set of specimens which first convinced me that the Stylasteridae were Hydroids and 
not Anthozoans, a fact which I had already been led to suspect from the structure 
observed in the case of a species of Astylus obtained from 500 fathoms off the Meangis 
Islands, and that of a Cryptohelia, a short reference to which was given in a paper “ On 
the Structure and Relations of certain Corals” (Proc. Roy. Soc,, No. 64, 1875, p. 64, and 
Phil. Trans., Yol. 166, Pt. I., 1876, p. 116). 1 have examined also other specimens of 
Stylasteridae obtained by the dredge and trawl of the ‘ Challenger ’ in various parts 
of the world, and a few specimens from those obtained by the United States dredging- 
expeditions, which have been generously placed at my disposal by Mr. Alexander 
Agassiz and Count de Pourtales of the Museum of Comparative Zoology of 
Cambridge, Massachusetts. 
Literature of the Subject. 
The family Stylasteridae was formed by the late Dr. Gray in his “ Outline of an 
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