GENERAL HISTORICAL INTRODUCTION, 



All siliceous Sponges in which the spicules belong to the triaxial type were, in 1870, 

 designated by Oscar Schmidt " Hexactinellidse." This title, which I would only modify 

 into Hexactiuellida, since the termination idas should be exclusively reserved for the 

 designations of ftimilies, soon found general acceptance, although Wyville Thomson had 

 previously established under the name of Vitrea an order of siliceous Sponges in which the 

 characteristic peculiarity was defined by the reference of all the spicules to the hexradiate 

 type. The older title proposed by Wyville Thomson has not gained currency, since 

 among the representatives of Vitrea enumerated by him forms occur in which the skeletal 

 elements are not referable to the hexradiate type, and which accordingly belong to another 

 order. 



Confining myself at this stage to a short review of the historical development of our 

 knowledge of the Hexactiuellida in general, I purpose subsequently to preface the 

 description of each genus with an accurate account of the relevant literature. 



First of all, there are a few isolated contributions of comparatively ancient date, which 

 give some account of certain structures which differed essentially in their peculiar form 

 and siliceous framework from any marine forms then known, but which, when subjected 

 to careful criticism, can be referred to certain now fairly familiar Hexactiuellida. Thus 

 Rozier's Journal de Physique for 1780, and a transcript from that work in the Magazin 

 fiir das Neueste aus der Physik und Naturgeschichte (published by Lichtenberg, Bd. 1, 

 Gotha), 1781, contain a description and a very characteristic representation of a form 

 belonging to the genus Dactylocalyx. This contribution, for an acquaintance with 

 which I am indebted to Dr. W. Marshall of Leipzig, is probably the earliest notice of a 

 Hexactinellid. In the Synopsis of the Contents of the British Museum for 1832, Gray 

 described a peculiar " glass rope like " structure preserved in the British Museum. This 

 he named Hyalonema, and described it carefully, though without recognising its real 

 nature as the basal tuft of a Hexactinellid. 



In the Voyage de "I'Astrolabe," 1833, Quoy and Gaimard figured and described, under 

 the name Alcyoncellum speciosum, a sponge form which undoubtedly belonged to the 

 Hexactiuellida. 



