DR. G. J. HINDE ON RECEPTACULITIDA. 819 
with which, however, it has, in my opinion, no relationship. His 
specimens only show the exterior surface, and from this he judges 
that the organism must be a “ Foraminifer like Receptaculites.” 
Ferd. Romer * states that the relationship of S. tessellatus, Phill., 
to Receptaculites cannot be doubted after Pengelly’s observations 
on its interior structure. He states, moreover, that Pengelly dis- 
covered in the interior of this form a canal-system consisting of 
horizontal and vertical tubes, thus regarding the ribs mentioned by 
Pengelly as canals. F. Romer rejects the term Spherospongia on 
the grounds that even if the fossil could be shown to belong really 
to Salter’s genus, yet, as the name indicates a relationship to 
Sponges, it is inappropriate ; he therefore proposed to substitute the 
term Polygonospherites instead. As, however, the type form seems 
to me to be a sponge, Rémer’s objection to its name loses its force. 
Genus AcantHocHoniA, Hinde, gen. nov. 
I propose this genus to include some shallow cup-shaped specimens 
from the Silurian strata of Bubowitz near Prague in Bohemia, where 
they occur in beds of the Etage E of Barrande. Though apparently 
very abundant, several specimens being oftentimes present in a single 
hand specimen of rock, only the outer surface is exposed to view; 
but, judging from the exceptionally favourable state of preservation 
of the surface of these cup-shaped examples, and the invariable 
absence of any traces of summit structures, there seems good reason 
for supposing that they retain their original and complete form. I 
have not, however, been able clearly to make out the natural 
margins of the cup, which are always enclosed by the matrix, and 
only indistinctly shown, even in vertical sections through the 
specimens. The base is either evenly rounded or with a shallow 
concavity in the centre; there is no trace of any attachment, and 
the forms were evidently free (Pl. XX XVII. fig. 2). 
The outer surface is composed of spicular plates, usually rhom- 
boidal in form, though in some cases the proximal and distal angles 
of the rhomboids are slightly truncate and the plate becomes 
approximately hexagonal. The outer or upper surfaces of the plates 
are flat, smooth, and exhibit the same horny-lustre as in the Djupvik 
examples of Ischadites. Concentric lines of growth are also apparent, 
though not so clearly marked asin Spherospongia ; and occasionally 
there are traces of a central knob-like elevation in the plates, as in 
this latter genus. At the nucleus or centre of the base there is a 
small circle of eight spicular plates arranged in a star-like form. 
The mode of arrangement of the plates in spiral curves, as well as 
the insertion of fresh rows, is precisely similar to what has been 
already described in Ischadites. The spicular plates fit at their 
margins, but not so closely as to preclude the possibility that a 
narrow channel may have existed between them originally, and this 
* Leth. Pal. Th. i. p. 297, fig. 54. 
