192 Dr. G. J. Hinde on Fossil Calcispongia. 
tailed descriptions of the Warminster Pharetrones and of two 
species from the Cretaceous strata of Vaches Noires, near 
Havre, in which the spicular structure of the fibre presents 1m- 
portant differences from that of the Warminster specimens. 
Verticillites D’ Orbignyt, n. sp. 
(BEX figs) 267, 8; Pl. Xl. fies: 1-245) 
The examples of Vertécillites which I propose naming FV. 
D’ Orbignyt are small club-shaped sponges from 16 to 23 
millim. in height, growing either singly or in small groups 
from a common base. Not infrequently new individuals’ 
spring from the sides or near the summits of others, as if by 
a process of budding. In some examples the base is con- 
tracted to a minute blunted stem; in others it expands to form 
a surface of attachment. Above the base is the first chamber, 
which is small and inconspicuous, and succeeded above by 
other subspherical chambers, arranged in single series, usually 
four to six in number. Each chamber is larger than the one 
beneath ; and the summit-chamber is conspicuously the largest. 
The chambers, excluding the summit, are each from 2 to 4°5 
millim. in height and trom 4 to 6°5 millim. in width; the 
summit-chamber is from 6 to 9 millim. in height and from 9 
to 14 millim. in width. The roof of each chamber in the 
series forms the floor of the one above it; and the different 
chambers are connected together by an interior tube passing 
through them. I have only been able to examine this tube 
in a single specimen, in which it appears to be imperforate. 
The summit of each chamber is depressed, dome-shaped, with 
a circular aperture in the centre, which in the summit-chamber 
is 2°25 millim. in width, and is bordered with a slightly elevated 
collar with smooth even margins. ‘The walls of the sponge 
are only °16 millim. in thickness, and appear to be formed of 
a single thin layer of fibre. The outer surface is smooth, and 
perforated with numerous minute circular or oval apertures, 
about °25 millim. in width and about their own diameters 
apart. These apertures open directly into the interior cham- 
bers. 
The fibres forming the wall of the sponge are entirely com- 
posed of spicules, apparently disposed in two layers—an outer 
or dermal layer, and beneath this the inner layer, forming the 
main portion of the fibre. I have obtained spicules from both 
these layers and mounted them in Canada balsam. Seen by 
transmitted light they are translucent, with occasionally a 
yellowish tint. Their outer surfaces have generally a rough 
eroded aspect, as if covered with a powdery coating of minute 
earthy particles, though probably this appearance is really 
