appear to exist. At present the results of the investigations of 
the sponges of the Challenger expedition are not known, : but 
recent investigations of the Atlantic sponges by Mr. Carter 
and those from the Gulf of Mexico by Oscar Schmidt show that 
the previous ideas as to the depth in which different orders of 
sponges exist, have to be considerably modified. The Mon- 
actinellidae and ‘Tetractinellidae were formerly regarded 
as inhabiting comparatively shallow waters, but it is now 
ascertained that they extend to depths previously thought to be 
exclusively inhabited by Lithistidae and Hexactinellidae; whilst, 
on the other hand, some representatives of these latter are 
now known to exist in but moderate depths. Two or three 
examples may be given of the depths in which existing. 
sponges nearly allied to those in the chalk, have been dis- 
covered. A species of Pachastrella, P. amygdaloides, Carter, 
whose spicules most closely resemble some in the Chalk flint, 
exists in the Atlantic at a depth of 1752 feet; Lyzdiam 
torguilla, O. Schmidt to which the chalk spicules of the 
same genus are nearly allied, also exists in the Atlantic, off 
the coast of Cuba, at a depth of 1610 feet; Lithistid sponges 
nearly allied to Racod?scula occur at varying depths between 
720 feet and 1620 feet; the Hexactinellidae are most abundant 
in depths between 1800 and 6000 feet, but a species of 
Cystispongia a genus also represented in the Chalk flint is 
recorded by Oscar Schmidt (Spong. d. Meerbusen von Mexico) 
as existing at depths varying between 120 feet and 1752 feet. 
So far as these comparisons extend, the sponges of this 
chalk flint may have inhabited depths of 1700 feet. | é 
The great resemblance which is presented by these 
Horstead sponge remains and the spicules which haye been 
described from the Haldon Green Sand; the Upper Chalk of 
the North of Ireland, the Chalk Formation of Westphalia, 
and the Eocene Sand of Brussels shows that these sponges 
had a wide distribution both in space and time. In_ the 
Eocene strata of Brussels there occur many forms of spicules 
