of Parkeria to Stromatopora. B55 
But whether the reticulated tissue of anastomosing, vermi- 
culated thread be infiltrated or not, the distinction between the 
tubes and this tissue is equally manifest, from the small size 
of the meshes of the latter contrasted with the much larger 
size and scattered position of the former, either on the surface 
of the fossil or in the vertical section, as they traverse the 
chamber ; at the same time if the surface alone be examined, 
then it does resemble that of the Polyzoa called “ Heteropora” 
(large and small tubes together) ; but this impression is soon 
corrected by an examination of the wninfiltrated or wnconsoli- 
dated specimen, when the “tubes,” which on the surface 
look like Heteropora, are seen to be separated by an inter- 
vening structure that, to my knowledge, hitherto has, in 
no shape, ever been found to occur with the cells of the 
Polyzoa. 
What, then, was the form of the animal that inhabited these 
tubes in the midst of the elementary structure of Parkeria, 
which is so totally different from that of the fossilized 
Polyzoa of the Coralline Crag, to which I might add those of 
the Coral Rag and the recent species of branched coralliform 
polyzoon, called “ Heteropora,” from New Zealand ? 
This question throws us back again upon the Hydroida, to 
which I have before alluded as presenting in the calcareous 
form the only kind of reticulated tissue mixed with large tubes 
(the calicles) for the use of the polyps or hydranths which 
have any direct resemblance to the structure of Parkerta (see 
‘ Annals,’ 1877, vol. xix. p. 50, pl. vii. fig. 5, &c.). 
If we assume that Parkeria was a polyzoon, then it must 
be entirely upon general resemblance and form, but not at all 
upon the elementary structure ; hence the assumption must 
be so far simply conjectural; while if we assume that it was 
a Hydroid, then we have in addition an almost identity in 
elementary structure to go upon for our assumption, and this 
being, under the circumstances, of the more consequence of the 
two, must be considered the more tenable. Besides, we have 
the instance of Chitina ericopsis (‘ Annals,’ 1873, vol. xi. 
p- 13), which, although dendritic in general form, is iden- 
tical in tissue with Parkeria, that is, the whole is elabo- 
rated out of a mass of continuous, anastomosing, reticulated, 
and vermiculated thread, without differentiation in any part 
beyond mere form; and although there are no ‘“ chambers ” 
here to be traversed by the “ tubes,” as in Parkeria, their 
analogues are to be seen in the form of hollow cylindrical 
processes or hydrothece at the ends of the branches, which 
tubes are composed of the same tissue and originally contained 
the polyps or hydranths. Now, were this “ thread” calca- 
