of the sponge remains, and at first led me to doubt whether 
they were spicules, but the presence of the interior canal 
points them out to be such. With one exception, in which 
there is a slight tapering at one extremity, all these spicules 
terminate abruptly, as if broken off at their ends, and therefore 
may be regarded as incomplete. One of the longest of these 
fragmentary spicules is 5,175 mm. long by 0,225 mm. wide, 
others are only 0,135 mm. in width, but their outer surfaces 
are so eroded that originally they may have been considerably 
thicker. It is quite a matter of conjucture as to the sponge 
of which these were the skeleton spicules, as, so far as I am 
aware, no sponge with similar spicules has yet been described. 
In Scoloraphis anastomans Zittel (Studien iiber foss. Spong. 
p. 95, Taf. XI, fig. 1) there are also sinuous spicules, but 
they are provided with knobbed surfaces, and are much smaller 
than these from Horstead. 
Order Tetractinellidae, Marshall. 
The characteristic spicule of this division of sponges has 
four arms or rays, one usually much longer than the others, 
radiating from a centre. Each ray is provided with an in- 
terior canal which unites with those of the other rays and, 
where the rays are bifurcated, the canal is also bifurcated and 
a branch extends into each division. There are two principal 
forms in which these quadriaxial spicules may be divided. In 
one there is a great development of a single ray, which _be- 
comes an elongated gradually tapering shaft, pointed at one 
end, whilst from the other and usually the thickest portion of 
the shaft, there spring three short arms or rays in very va- 
rying directions; in some spicules prolonged backwards, fork 
like, nearly in a line with the shaft itself; in others, at varying 
angles between the perpendicular and horizontal ; whilst in other 
spicules. the rays curve backwards, in the direction of the 
point of the shaft, and become anchor-shaped. These three 
