Mr. Tl. J. Carter on the Hexaotinellida*. 351 



diate spicules characterize one, a trifid branching of the shaft 

 or quadriradiate form characterizes the other system. 



In 1868, Prof. Wyville Thomson's classification of these 

 sponges appeared under the name of " Vitrea," to which Prof. 

 Thomson added what Dr. Gray had excluded from his Coral- 

 liospongia, viz. the sarcospiculous Hexactinellidae (ex. gr. 

 Hyalonema &c.) — that is, the Hexactinellidse which are not 

 vitreous (Annals, vol. i. p. 119, Feb. 1868). 



But in his fifth genus Prof. Thomson also includes the two 

 species mentioned under the head of " Dactylocalyx" viz. 

 " Dactylocalyx pumicea [pumiceus ?], Stutchbury, and Dacty- 

 localyx azorica, Gray ," ' = MacAndrewia azortca, Gray. (See 

 also Prof. Wyville Thomson's " genus 4," Phil. Trans. 1869, 

 pt. ii. p. 713.) 



At length, in 1870, the results of Schmidt's examination of 

 the deep-sea sponges sent to him from America were published 

 (' Grundziige einer Spongienfauna des atlantischen Gebietes '), 

 in which the two systems are respectively recognized under 

 the heads of" Hexactinellidge " and "Lithistida? " — the former 

 for the sexradiate, and the latter for the triradiate type, our 

 quadriradiate system. The result of this examination shows 

 plainly how much more Schmidt would have done with these 

 systems with more time and more material at his disposal. 



I had noticed this distinction before seeing Schmidt's work, 

 in my " Fossil Spicules of the Greensand " (Annals, vol. vii. 

 pp. 117, 118, Feb. 1871), where, instead of the term "tri- 

 radiate," I had proposed " ternate " &c. ; but without reference 

 to this in particular, it will be easily seen that if we are to 

 call those sponges A&ractinellid whose central canal at one 

 point consists of six arms, the other group, whose central 

 canal at one point consists of four arms (viz. that of the 

 shaft and its three branches together), should be termed 

 " qitadrir&disde " to be consistent. The term " triradiate " 

 does not suffice for the latter, which must be either " quadri- 

 radiate " or, as I had before proposed, " ternate " or " trifid." 



Then, again, if we adopt " ternate " or " trifid," to be con- 

 sistent we must change " hexactinellid " to " quinate " or 

 " quinquefid ;" for in the larger-headed spicules of the Hexacti- 

 nellida? the shaft is often so marked that we have to describe 

 it under this term, while the minute sexradiate spicules being 

 for the most part equiaxmed, no other term can be used for 

 them than " sexradiate." 



I have endeavoured to show that in the development of a 

 sponge-spicule which is not equiradiate, the primary form 

 is a straight line, from whose central canal branches are 

 subsequently given off to form the rest of the spicule proper 



24* 



