826 DR. G. J. HINDE ON RECEPTACULITIDA. 
considerably from that of RR. occidentalis. He states that the 
vertical spicular rays (Siulchen) increase in thickness towards the 
inner integument, near to which they contract and again expand to 
form a support to the calcareous plate proper of the inner layer. 
The expansion however is not decidedly four-armed, but a greater 
number of thicker irregular branches, with apparently lateral 
branchlets, radiate from the pillar. These are not united by growth 
with the main plate. Small canals also run through the plates, 
though they are only recognizable with difficulty. Thus the plates 
of the inner integument consist of a principal calcareous layer and 
a radiating under layer extending from the pillars. There is also a 
very thin surface layer of daik carbonaceous material resembling that 
of the outer integument, but with a distinctly marked granular 
surface. Giimbel further states that, after repeated careful obser- 
vations, he is firmly convinced that there does not exist any perfora- 
tions in the angles of the plates of the inner integument of R. 
Neptunt, and that these perforations cannot be considered as one of 
the characters of the genus. He thinks, however, that communication 
with the exterior took place by means of small channels between 
the sutures of the plates. into which also the branching canals from 
the pillars certainly extended. 
Notwithstanding the apparently fundamental differences in the 
structure of the inner layer of A. occidentalis and that of R. Neptuni, 
T am still of opinion that the characters shown in the silicified 
examples of the former species probably represent with greater 
accuracy those of the genus than those which Giimbel has described 
in R. Neptuni. It is quite possible that in the replaced calcified 
specimens, which can only be seen in sections or etched surfaces, the 
real characters of the inner layer may be so concealed or altered as 
not to be recognizable, and that therefore greater dependence should 
be placed on the silicified examples, in which all the other characters 
of the organism are better preserved than in the examples with 
skeletons of crystalline calcite. 
The characters of the genus Receptaculites may be briefly summed 
up as follows :—Cup- or platter-shaped bodies of considerable size, . 
with walls of definitely arranged spicules. The outer surface is 
formed by the rhomboidal head-plates of the spicules ; beneath these 
are the horizontal rays, and robust subcylindrical vertical rays, 
which are connected with an inner layer or perforated plate. 
Communication with the exterior was carried on between the mar- 
gins of the summit-plates of the spicules on the outer surface, and 
through the cylindrical canals of the inner surface layer, or, accord- 
ing to Giimbel, through intermarginal canals. 
From all the other genera of the femily, Receptaculites is distin- 
guished by the possession of an inner layer. 
It seems unnecessary to give a detailed history of the genus, 
since this has been sufficiently shown in the previous part of the 
paper. By the earlier authors, Defrance and Kichwald, the hollow 
casts of the vertical spicular rays were regarded as polyp-cells and 
the form was placed amongst the Corals; it was next placed by 
