8 



On the HexactinellidjE. 

 By B. W. Priest. 



Read May 23rd, 1884. 



PLATES II., III. 



The order of Sponges to which I wish to draw your attention this 

 evening, and to which I briefly alluded in a former paper on the 

 Histology of Sponges generally, is one which comprises some of the 

 most interesting, as well as the most beautiful in structure of that 

 class of the Animal Kingdom. 



As early as 1833 two or three forms were already known and 

 described, first by MM. Quoy and Gaimard, and subsequently by 

 Stutchbury and others. 



But it was not until the results of the deep-sea explorations 

 which were instituted between the years 1860 and 1870, and 

 followed up to the present time, became known, that any idea of 

 the number of species of that order were arrived at. 



Some of the species are now pretty well known, being repre- 

 sented in several of our museums by the so-called Venus' Flower 

 Basket, the Glass rope Sponge, the Birds' nest Sponge, and 

 others, all of which were well displayed at the late Fisheries Ex- 

 hibition, and most of the typical species are now to be seen at the 

 Natural History Museum at South Kensington. 



In 1867 the late Dr. Gray proposed the term Coralliospongia 

 for the order. This answered at the time, as most of the sponges 

 then known and comprised under that arrangement were hard and 

 coral-like, the skeleton entirely formed of siliceous spicules anchy- 

 losed together by siliceous matter, forming a netted mass covered 

 with Barcode. When, however, other forms were found, it became 

 necessary to alter this classification. Dr. Oscar Schmidt proposed 

 to distinguish the whole series under the title of Hexactinellidce, 

 from the fact that all the species shared in common the possession 

 of hexradiate spicules. 



In 1870 Mr. Saville Kent took the same view, placing Dr. 

 Gray's name, Coralliospongice, as a sub-order to Dr. Schmidt's pri- 



