34 

 Geodia? sp. 



(Plate III. figs. 3, 6, 7, 9;- 



Moderately robust, simple and compound trifid spicules, 

 with elongate, straight or slightly curved shaft. The head rays 

 of the simple forms are short, conical, pointed and directed 

 obliquely forwards; in the compound spicules the rays are 

 stouter and more compressed, with the primary rays directed 

 forward, but the secondary bifurcations extend in a horizontal 

 direction. There are considerable differences in the dimensions 

 of these spicules and the figures represent specimens of the 

 average largest of each form. The smallest (fig. 9) has a 

 length of 1.28 mm.; thickness of shaft 0,135 mm.; and 

 width of head rays 0,405 mm. The larger, (fig. 3) has a 

 length of 3,15 mm.; width of shaft, 0,22 mm. and width of 

 head rays 0,742 mm. There are a number of examples of 

 each of the four forms which I have figured and the exam- 

 ples of each form correspond pretty closely in size, so that 

 it is quite possible that they may belong to more than one 

 species of sponge. Spicules similar to these occur in other 

 groups of sponges besides Geodia and genera allied to it. 

 Thus a form similar to that placed under fig. 3 is found in 

 OphirapJiidites cretaceus, Zittel (Stud. lib. foss. Spong. p. 98, 

 Taf. XI, fig, 2 d) and it is also present in great numbers in 

 the Lithistid sponge Dorydernia dichotoma, Roemer, sp. (Stud, 

 lib. foss. Sp. Taf. VII, fig. I c) but as none of the spicules of 

 the mesh of Doryderma are found in the flint-meal, these tri- 

 fids are not likely to have belonged to this species. Similar 

 spicules are very abundant in the Haldon Green Sand and 

 are included by Mr. Carter under the name of Geoditcs hal- 

 donensis (An. and Mag. Nat. Hist. Vol. VII, PL X, figs. 60, 

 61, 63, 66): they have also been figured by Zittel from the 

 Upper Chalk of Coesfeld. (Ueber Coelop. Taf. VI, fig. 6, 9, 

 Taf. VII, figs. 2, 3, 6). 



