DR, G. J. HINDE ON RECEPTACULITIDA. 823 
are only united with the summit-plate at the common centre of the 
spicule, as distinct from the summit-plate itself. 
The horizontal rays, the equivalents of the stolons of Billings, the 
Stiitzarme or Hpistyle of Gtimbel, are only seen when the summit- 
plates of the spicules have been partially or entirely removed by 
natural or artificial means, and they then appear as four short rays 
radiating from a common centre, which also coincides with the 
centre of the head plate. Their arrangement is precisely similar to 
that in Ischadites, but they are very much smaller and slenderer 
in proportion to the dimensions of the vertical ray of the spicule, 
than in this latter genus, and consequently less resemble normal 
hexactinellid spicules. The horizontal rays of each spicule, as in 
Ischadites, are distinctly free from the rays of adjoining spicules, 
and very frequently they overlap each other and rest side by side. 
This fact is clearly recognized by Giimbel*; but Billings supposed 
that they were connected with the rays of adjoining spicules, though 
they are shown in his diagram as meeting each other, but not in 
contact. 
In the silicified specimens of Ff. occidentalis from which Billings’s 
description was taken, the extremities of the spicular rays appear 
to be invariably incomplete after treatment with acid, so that he had 
himself no opportunity of observing their natural termination. In 
the same specimens, the peculiar fact is shown that the horizontal 
spicular rays are not all strictly in the same plane, or at right 
angles to the vertical ray, for while this is the case with the lateral 
rays, the distal and proximal rays are slightly oblique, so that 
the proximal ray, or that pointing to the nucleus, projects 
slightly upwards, while the distal or opposite ray extends slightly 
downwards (Pl. XX XVII. figs. 31, m). The four horizontal rays 
are traversed by axial canals, which unite with each other and with 
the canal of the vertical ray at the central point of junction of the 
spicule. I have not been able to detect more than four horizontal 
rays with their corresponding canals in any of the specimens of 
R. occidentalis, and Giimbel refers to four only in the specimens 
which he examined; but in the cast of a specimen from Ober- 
Kunzendorf figured by Damest, and which through the kindness of 
Prof. F. Romer I have had an opportunity of seeing, there are, in 
addition to four well-marked horizontal rays, small subordinate rays 
apparently radiating from the central point of junction of the 
spicule, in a similar manner to those of certain spicules of Holas- 
terella, conferta §, Carter. 
Jt will not be necessary to again describe the different aspects of 
the surface of the organism in different conditions ,of fossilization, 
since the subject is referred to in treating of Jschadites, and there 
is no difference in the aspect of Heceptaculites under similar con- 
ditions ; but whilst no silicified examples of the former genus are 
known, they are not uncommon in one species of Recepitaculites 
* Beitr. p. 29, t. A. fig. 4 0d. | t Pal. Foss. vol. i. p. 380. 
t Zeitsch. d. deutsch. geol. Gesellsch. Bd. xx. p. 484, t. 10. f. 1. 
§ See Cat. Foss. Sponges, Brit. Mus. p. 152, t. 32,f.2. 
312 
