32 THE VOYAGE OF H.M.S. CHALLENGER. 



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 Crijptohelia, 

 a short reference to which was given in a paper On the Structure and Relations of 

 Certain Corals (Proc. Eoy. Soc, No. 64, 1875, p. 64, and Phil. Trans., vol. clxvi., 

 part 1, 1876, p. 116). I 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. I have also 

 examined specimens of Distichopora preserved in spirits, which I obtained from the 

 Museum Godeffroy. 



Literature of the Subject. 



The family Stylasteridae was formed by the late Dr Gray in his Outline of an 

 Arrangement of the Stony Corals (Ann. and Mag. Nat. Hist., vol. xix. p. 127, 

 1847). The family was made to contain the genus Stylaster alone, and was thus 

 characterised : — 



" Coral minutely porous, cells deep, cylindrical, with six grooves, each ending in a 

 pore and a central style." 



MM. Milne-Edwards and Haime placed Stylaster in a sub-family Stylasteraceae, from 

 which, however, they excluded Errina and Distichopora, although they included Axohelia, 

 which is a Mddracis. 



Count de Pourtales, in his Deep-Sea Corals (Illustrated Catalogue of the Museum of 

 Comparative Zoology at Harvard College, No. 4, 1871, p. 33), writes as follows : — 



" Professor Verrill first recognised the close affinity of Distichopora, Errina, and 

 Stylaster (Bull. Mus. Comp. Zool., No. 3, 1864). In his Notes on the Radiata (Trans. 

 Conn. Acad., vol. i., 1870) he adopted a suggestion of mine to make a distinct family 

 of the Stylasteridae, which he places in his sub-order Oculinaeca, both of us overlooking 

 the fact that Gray had already established it." 



Pourtales, struck by the porous nature of the ccenenchym of the coenostea of the 

 Stylasteridae, and other points in the hard structure which he observed, removed the 

 Stylasteridae from amongst the imperforate corals, and ranged them next to the Eupsam- 

 midse. He fully recognised many strong points of affinity which rendered the family a 

 natural one, but failed to ascertain the true character of the organisms, because he had 

 not opportunity of examining their soft structures. 



