MR. S. O. RIDLEY ON THE GENUS DIRRHOPALUM. 



487 



spined ends, might have been taken for an extreme form of dumb- 

 bell spicule but for Carter's observations, described and supported 

 by Sollas (Ann. & Mag. N. H. (5) vi. p. 394), which tend to show 

 it to be merely a foraminifer-cast. 



Further, Mr. G-. J. Hinde, in his inaugural dissertation en- 

 titled ' Fossil Sponge-Spicules from the Upper Chalk' (Munich, 

 1880), figures at pi. i. figs. 19, 20, two spicules of about the 

 same contour as the "pegtop" form of J), clopetarium, but 

 without tubercles, and of about three times the size of that 

 spicule. The tubercles may have been lost by absorption, for 

 the central canals are greatly enlarged. Fig. 22 of his paper 

 represents a similar but slightly smaller spicule, provided, how- 

 ever, with tubercles tending, as in D. clopetarium, to disappear 

 towards the point, which is broken off. Mr. Hinde refers to D. 

 {Plocarnia) gymnazon and clopetarium among other Sponges in 

 connexion with some accompanying large acuates (p. 21, pi. i. 

 figs. 10-15) ; but they can have, taken alone, no necessary con- 

 nexion with those species, although occurring in conjunction 

 with the conical types above mentioned, they seem to show very 

 conclusively the existence of a Dirrhopalum of the clopetarium 

 section in the seas of the Chalk period. 



A. Eutot (Annales Soc. Malac. Belg. ix. pi. iii.), at fig. 7 figures 

 a dumbbell spicule, at fig. 6 an elongated smooth pegtop form, 

 and at fig. 39 a a cylindrical, from the " G-res " of the lower and 

 middle Brussels strata (Eocene). 



We have, then, for the distribution of the genus in time as 

 at present known : — 





-1-3 

 fl 



<D 

 O 



U 



$-1 

 0> 



EH 



o 



M 



i— i 

 c3 



o 



u 



o 

 t-3 



a 

 d 



<v 



o 



D. gymnazon group 



* 

 * 



* 

 *? 



* 





# 



D. clopetarium group 





