Nodules of the Trimmingham Chalk. 391 



but in general form these appear to be different. He gives 

 them as coming from a Pachastrella-Yike sponge ; ours pro- 

 bably are also derived from a Pachastrellid genus. 



Dercitites haldonensis } Carter. 

 (PL XX. figs. 41 & 47.) 



Carter, Fossil Spicules, loc. cit. pi. x. fig. 71. 



These, as Carter has pointed out in speaking of the similar 

 spicules from Haldon, are essentially similar to the quadri- 

 radiate spicules in Dercitus Bucklandi, Bow. They cannot, 

 however, with certainty be referred to this genus, since O. 

 Schmidt has discovered similar spicules in a Lithistid sponge, 

 Collectella avita (Mex. Spong. Taf. v. fig. 1, p. 86). 



Geodites cretaceus. (PI. XX. fig. 34.) 



Geodites haldonemis (in part), Carter, Fossil Spicules, loc. cit. pi. x' 

 figs. 59, 62, 09. 



This is evidently the globate of a Geodine sponge. It has 

 lost all trace of tubercles and internal structure, owing to 

 changes produced by mineralization ; but the hilum is still 

 clearly shown. 



Such globates are abundant in the deposit, varying in dia- 

 meter from -Jy to yi-g- inch ; it is possible that they may belong 

 to more than one species. 



The largest forms are bigger than those of G. Macandrewi, 

 in which they attain the largest size known amongst recent 

 sponges. It is, however, with the globates of G. Macandrewi 

 that these fossil forms best agree ; and the trifid spicule with 

 bifid rays of fig. 43, and the similar but also Stelletta-like form 

 of fig. 55 are both so similar in character to the corresponding 

 spicules of G. Macandrewi, that we may, with great plausi- 

 bility, associate them with the globate, while the forms shown 

 in figs. 35 and 43 are sufficiently similar to the anchors with 

 projecting and recurved rays occurring in this sponge to go 

 in the same grouping. 



Thus figs. 34, 35, 36, 37, 43, and 45 may be regarded as 

 having probably been derived from one species of sponge, to 

 which we may give the name Geodites cretaceus. 



The opportunity may be taken to add here a few words on 

 fossil globate spicules in general. They were first discovered 

 by Carter, and described in his paper on fossil sponge-spicules 

 before quoted. Zittel* figured them in connexion with Ccelo- 

 ptychium ; and his specimens are of great interest as presenting 

 the various stages of dissolution which may be observed in 



* Zittel, Cozloptychium. 



