202 Dr. G. J. Hinde on Fossil Calcispongie. 
A thin transverse section presents under the microscope 
substantially the same spicular structures of the fibre as in 
the preceding species, and therefore it will not be necessary 
to repeat the description of them in detail. Some represen- 
tations of the spicules of the fibre are given on Pl. XII. figs. 
16-24. In fig. 16 are represented portions of the sagittal and 
basal rays, and the truncated base of the apical ray, of alarge 
quadriradiate spicule. The lateral rays of this spicule appear 
to have been curved in a similar manner to those of a large 
triradiate in Leucetta pandora, Hick. (Mon. Taf. xxii. f. 
m, é). Portions of smaller tri- and quadriradiates are shown 
in figs. 17, 18. The fork-shaped spicules (figs. 20, 22-24) 
closely resemble those of S. rugosa. ‘There is also a small 
irregular triradiate (fig. 21) which is precisely-similar to one 
figured by Hiickel in L. pandora. 
In addition, however, to this spicular structure of the fibre, 
the type specimen of this sponge exhibits spicules on a small 
smooth oblong space on the under surface, which I have 
already mentioned as indicating the part on which the sponge 
rested during its growth. This spot, 10 millim. long, by 
5 wide, is smooth and non-perforate, and is thickly covered by 
a layer of triradiate spicules, irregularly disposed, with the rays 
crossing each other (fig. 25). ‘These spicules are sufficiently 
large to be seen with a simple lens ; they vary in size; a fairly 
large specimen has the rays ‘2 millim. long. It is very pro- 
bable these spicules possess an apical ray penetrating into the 
interior and are thus really quadriradiates ; but I am unable 
to determine this point. In form they are either sagittate or 
subregular, ¢. e. having the arms nearly of an equal length 
and the angles subequal. These spicules, thus apparently 
restricted to this small part of the exterior surface, closely cor- 
respond to the dermal spicules which in Verticillites and Cory- 
nella form a layer over the entire outer surface of the sponge. 
Notwithstanding the similarity in the spicular structure of 
the fibre to S. rugosa, the form and proportions of the mass 
and of the component individuals differ sufficiently, im my 
opinion, to permit this form to be. regarded as a distinet 
species. ; 
Horizon and Locality. Cretaceous, Vaches Noires, near _ 
Havre. 
Collection. British Natural-History Museum. 
From the close similarity which has been shown to exist 
‘between the minute spicular characters of the five species 
above described and those of existing Calcisponges, it seems 
to me that the originally calcareous composition of the fossil 
