the Qreensand compared with those of existing Species. 133 



abounds in Discodermia polydisciis (Schmidt's mounted speci- 

 men of Corallistes ptolydiscus in the British Museum). 



As this spicule is a simple or smooth analogue of Monilites 

 haldonensis, so there is a simple one of M. quadriradiatus^ 

 which I have not figured, but which is equally plentiful with 

 the latter in the Haldon deposit, and therefore equally de- 

 serving of notice. 



Figs. 48, 49, and 57 are all abundant, but with no character 

 to associate with any existing species in particular. Although 

 small, they are much larger than most of the spicules of 

 existing shore Sponges, excepting the- Pachytragife. 



Figs. 50, 51, and 52 are respectively peculiar in form, but, 

 apart from the sponges to which they belonged, are of no 

 specific value. Their figures are introduced here as represen- 

 tatives of a great variety of the same size which exist in the 

 Haldon deposit. In fig. 52, which is the smallest spicule with 

 definite form that I have fovmd, we seem to have a capitate ray 

 of one of the minute hexactinelled (" floricomo-hexradiate," 

 Bk. B. S. pi. 8) spicules in the Coralliospongife ; but this is 

 all that can be said for it. In some instances it is as probable 

 that the minute spines or projections of a spicule may have 

 been obscured by chalcedonic union into one mass, as that the 

 solvent influence may have carried them off altogether. 



Last, although far from being the least important, are figs. 

 55, 56, which represent one of the globular crystalloids or 

 siliceous balls of the crust of a Geodia. Perhaps, from its 

 specific value and great abundance, it is one of the most in- 

 teresting forms in the deposit. That represented in figs. 55, bQ, 

 which give its lateral and upper profiles respectively, is the 

 average size of the largest, and shows that it is somewhat de- 

 pressed or a little less in diameter vertically than it is laterally, 

 also that it possesses the usual hilous depression below. 



These little balls not only form the crust of the existing 

 Geodida3, but are scattered more or less throughout the whole 

 structiu-e of these sponges, where they present as many sizes 

 as phases of development, which may thus be followed from 

 the youngest to the most matured state (see their structure &c. 

 'Annals,' 1869, vol. iv. pis. 1 & 2). They are therefore ex- 

 ceedingly numerous; and, fm'ther, in the existing species, they 

 somewhat differ in their globular forms and in the markings 

 or pattern on the surface of the matured ones. 



Hence it is not suprising that they should be very abundant 

 and be present of different forms and sizes in the Haldon de- 

 posit ; but the pattern on their surfaces is so obscured by the 

 minute botryoidal crystallization of the chalcedony before 

 mentioned, that I have only met with one instance in which 



