130 Mr. H. J. Carter 07i Fossil Sjwnge-spicules of 



a species of Geodia with the hexternate or furcate spicule of 

 Htelletta and the siliceous balls of a Geodia, in which case the 

 genera of Schmidt's groups of Ancorinidte and Geodidinse 

 would come together. 



Lastly, we come to the simple ternate or trifid head of the 

 long-shafted spicules, of which three kinds at least, with their 

 varieties, abound in this deposit, viz. fig. 70, which is very- 

 stout, with long shaft and three arms expanded laterally, 

 almost horizontally, and a little recurved. In the illustration, 

 which is taken from the most perfect one that I could find, 

 the arm on the left side is broken off square, and the other 

 two, which were about equal in length, broken or rounded off 

 by attrition. Fig. 36, PI. IX., also belongs to the simple 

 ternate division of the head with long shaft ; but the arms are 

 more or less straight, elongate, attenuated, and spread out at 

 equal distances from each other, somewhat forwards. Fig. 71 

 is another of this kind, but frequently with very little differ- 

 ence between the length of its shaft and the expanded arms. 



Of these the two former, viz. figs. 70 & 36, miglit, from the 

 length of their shafts, have belonged to the circumferential 

 spicular zones respectively of two different species of Geodia. 



But the prevalence of fig. 71 and its varieties, chiefly in 

 size, so nearly resemble the stout spicules with which an 

 existing species, viz. Dercitus niger (Annals, Jan. 1871), is 

 densely charged, that I do not think that a more appropriate 

 appellation can be assigned to it than that of Dercites haldo- 

 nensis. 



The existing type grows on the rocks at Budleigh-Salterton, 

 and is a black variety of Hymeniacidon Bucklandij Bk.,= 

 Pachastrella Buchlandi, Sdt. 



We now leave the spicules of the ternate system, and go 

 to that large acerate form whose middle and ends are repre- 

 sented in PI. X. fig. 76, a a, which, with the exception of 

 Dercitus niger (which is peculiar in this respect), is the cha- 

 racteristic body-spicule of all the known Pachytragiae ; and 

 hence its great abundance of different sizes in the Haldon 

 deposit is easily understood. It is smooth, acerate, fusiform, 

 and for the most part stout and slightly curved, as shown in 

 the figure, which otherwise represents the average size of the 

 largest specimens. 



The same remarks apply to the acuate spicule, whose large 

 and small ends are given in fig. 77 a, but with this exception, 

 that the acuate form is somewhat smaller and less abundant 

 in the existing species as it is in the Haldon deposit. It seems 

 also to be but a modification of the body-spicule, in which one 

 half is shortened and enlarged at tlie expense of the length of 



