29 



tions, in other instances they are bow-shaped or curved in 

 the form of the letter C. One of the largest specimens is 

 3,8mm long by 0,13 mm wide; an average specimen measures 

 2,25 mm long by 0,09 mm. wide. They are very abundant. 



These spicules correspond pretty closely with those which 

 Mr. Carter discovered on the outer surface of some Atlantic 

 sponges, to which he has provisionally given the name ol 

 Ophirapkidites tortuosus, it being at present doubtful whether 

 they may belong to a distinct sponge or whether they are the 

 acerates of a species of Pachastrella. (An. Mag. N. H. Dec. 

 1876 p. 458). Similar spicules are also present in the Haldon 

 Green Sand, (An. Mag. N. H. Vol. 7 p. 131 PI. X. fig. 79); 

 in the Westphalian Chalk, (Ueb. Coelop. Taf. IV. fig. 24, 25) 

 and in the Eocene sand at Brussels. (Rutot: op. cit. PI. 3, 

 figs. 5, 29). 



Simple and Compound Trifid Spicules of Geodia and 



allied Genera. 

 Geodia? clavata n. sp. 



(Plate I. fig. 4. plate II. figs 15.) 



Very robust spicules with an elongate, straight or slightly 

 curved shaft, constricted immediately beneath the head ; below 

 this, there is a bulbous inflation from which the shaft gradually 

 tapers to a point. The head rays in all the simple forms, and 

 in some of the compound as well, are but little more than 

 short rounded knobs (fig. I 35); in other compound heads 

 the rays are more compressed and bifurcate into small pointed 

 extensions. In some instances the number of the rays is 

 limited to two. (fig. i). The interior canal of the shaft is 

 partially preserved ; in some spicules it may be seen to extend 

 throughout the entire length; in others only traces of it are 

 exhibited in the inflated portion of the shaft, where it is 

 expanded in the same manner as the shaft itself. Very 

 rarely are canals exhibited in the head rays. In some spicules, 

 which at first I thought might be acuate spicules with bul- 



