438 
DR. G. J. HIXDE OX BEDS OF SPOHGE-REMAIHS IX THE 
Slender bihamate spicules with short obliquely incurved extremities. Length '533 bv 
‘041 mm. in width. It may be doubted whether these forms are really analogous to 
the bihamate spicules of the existing genus Esperia, since, as Mr. Carter has already 
remarked, they are five times the size of the recent spicules, 
U. G. S., Blackdown, Merstham. 
12. Dirrhopalum neocomiensis (Plate 41, fig. 14). —Robust, smooth, straight, conical 
spicules, with an inflated, evenly-rounded summit, a slight constriction immediately 
beneath; from this, a gradual tapering to a sharply-pointed extremity. Length 
] ‘22 mm., greatest width '275 mm. The affinities of this form are very doubtful; it 
may have some relationship to the smooth conical spicules in the upper chalk, which 
I have named Dirrhopalum planum , and I therefore include it provisionally in the 
genus. 
L. G. S., Haslemere. 
13. Hamate spicule (Plate 41, fig. 18).—A smooth, cylindrical, hamate spicule, 
apparently perfect. Length ’366, by '06 mm. in width. I do not know of any fossil 
or recent spicule at all similar to this. 
L. G. S., Haslemere. 
14. Anomalous acerate spicule (Plate 41, fig. 12).—Minute, smooth, a cerate spicule, 
evenly cylindrical for the greater portion of its length, then tapering. One end is 
acute, the other obtuse. This exterior acerate form appears to inclose a spinulate 
form with a pear-shaped head and straight shaft, and within this is a central axial 
rod which seems to be the infilled canal. Length '12 mm., width ‘018 mm. The 
affinities of this peculiar spicule are doubtful. It is the smallest form which I 
have discovered in the sponge-beds, and only one example of it has been met with. 
U. G. S., near Warminster. 
Order Tetractinellidce Marshall. 
The distinguishing characters of the recent genera, Geodia, Stelletta, Erylus, and 
other allied forms, are based on the structural features of the dermal layer. In the 
greensand sponge-beds there are numerous examples of zone and anchor spicules, 
together with body acerates and the globates and globo-stellates of the dermal layer, 
but in their detached condition it is impossible now to determine the particular zone- 
spicules which may have been associated with the dermal spicules, and thus there can 
be no certainty in assigning the various forms of the zone-spicules to one or other of 
these genera, and it may therefore be desirable to adopt Carter’s general term 
Geodites. In recent sponges of this group, the species are characterised by a dis¬ 
tinctive zone-spicule, and in like manner the different forms of these fossil zone- 
spicules may be regarded as indicating distinct species. The differences in the 
acerate spicules of distinct species are not recognisable in the fossil detached spicules, 
and they will have to be considered in a single group. 
