from the Middle Lias of Northamptonshire. 357 
Middle Lias, in the zone of Ammonites spinatus, at King’s 
Sutton, Northamptonshire. Associated with the sponges are 
numerous specimens of well-preserved Foraminifera, Corals, 
Mollusca, and Polyzoa; these latter have already been 
described by Mr. Walford (Quart. Journ. Geol. Soc. vol. xliii. 
1887, p. 636). 
II. Detached Calcisponge Spicules in the Upper Chalk 
of Surrey. (Pl. XVII. fig. 10.) 
In some mountings of the finer material of the Upper Chalk 
(zone of Micraster) from Croydon and Sutton, Surrey, there 
are, in addition to the common Foraminiferal species of Tewx- 
tularia, Globigerina, &c., some minute three- and four-rayed 
spicules, very similar in appearance to those of ordinary 
Calcisponges. The spicules are of calcite, their forms are 
fairly complete, but their surfaces are rough and uneven, as 
if covered by the finest particles of the Chalk. The rays are 
conical, with blunt terminations ; they vary from ‘04 to °13 
millim. in length and from ‘007 to °02 millim. in thickness. 
Some are regular forms with rays equal in length; in others 
the rays are unequal. Beyond some rod-like fragments of 
the same thickness as the three-rayed forms no other spicules 
are present in the material. As these spicules correspond in 
form, size, and mineral structure with those of Calcisponges, 
it seems reasonable to conclude that they are detached from 
sponges of this group. The only other inference is that they 
may be spicules of siliceous ‘Tetractinellid sponges which 
have been replaced by calcite. But against this supposition 
is the fact that even the larger forms of true siliceous spicules 
are very rare in the Chalk of these areas (unless included in 
the cavities of flints); they have been dissolved, leaving 
empty moulds in the chalky matrix. Further, in these spicules 
the three facial rays are approximately in the same plane, the 
same as those of Calcisponges generally, whereas in the 
Tetractinellid Calthrops spicules the rays are generally dis- 
posed in the form of a tripod. It would also be very unusual 
to find such very small detached forms which had undergone 
mineral replacement. As Calcisponges of the genus Hlasmo- 
stoma are found in the Chalk of Kent, the occurrence of 
detached spicules might have been anticipated ; but they do 
not appear to have been noticed previously. 
