698 MESSES. P. MAETIN DUNCAN AND H. M. JENKINS ON PALiEOCOEYNE. 
contact with a moving body would have fractured them. There is much diversity in the 
length of the tentacles and in their thickness, and most of them are marked with trans- 
verse cracks, the result of post-mortem violence. 
The distal ends of the longest tentacles are very delicate, yet a long ciliated process 
might pass out from the free termination as in Bimeria vestita. The metastome is 
visible in a specimen of both species ; but usually the granular polypary of the oral 
surface shows no opening, and it is only when the exact spot of the mouth is worn down 
to in sections that any trace of it can be found. The ridges of this surface are usually 
connected by festoon ornamentation. 
The development of the periderm of the hydrocaulus from the ccenosarc may be in- 
ferred ; for in longitudinal sections there is an appearance of horizontal striation, and 
the striae indicate the former projection into the periderm of processes belonging to the 
ccenosarc. 
VIII. Palaeontological relations. — Although the Hydrozoa are very abundant in fresh 
and in sea-water, they are very rarely found as fossils. Their delicate structure and 
peculiar periderm would prevent their fossilization under ordinary circumstances. 
M. Fischer* has distinguished Hydractiniae in the Cainozoic deposits of Dax and in 
the Cenomanien of Mans ; and the impressions of Medusae have been discovered in the 
Jurassic strata of Solenhofen. 
In the Silurian division of the Palaeozoic strata are the fossils called Graptolites, which 
are considered by some Palaeontologists to be Hydrozoa. The theory announced by 
Agassiz respecting the Hydroidean characters of the tabulate division of the Sclerodermic 
Zoantharia is still under consideration and requires confirmation. 
The interest of the discovery of the Palceocorynidce in the moderately deep-sea depo- 
sits of the Carboniferous period is therefore great. The form of the Medusae of the 
species is of course unknown, but it is evident that they floated in the estuaries and 
shallow seas, and perhaps in the oceans of those Palaeozoic days, and deposited the ova 
which produced the trophosomes that have descended to the present time in a fossil con- 
dition. 
The choice by both species of the margin of a polypary of Fenestella for their resting- 
place, suggests that some portions of the economy of the Polyzoon were beneficial to 
their more or less rigid associates. Doubtless the gentle movement of the frond-like 
mass and the currents produced by the numberless polypes contributed to the supply of 
food for the Hydrozoa. The ornamentation of the Fenestella is occasionally repeated on 
the tentacles of the Palceocoryne Scoticum in a very striking manner. 
Note. — The calcareous investment of Palceocoryne Scoticum and Palceocoryne radiatum 
has not the peculiar cleavage of the hard structures of the Echinodermata. — September 
6 , 1869 . 
* Bull, de la Soc. Geol. de France, 2 serie, tome xxiv. p. '689. 
