ON RHORONIS OVALIS, STRETHILL WRIGHT. 
117 
as the structure could be made out in the part of the animal 
protruded from the membranous tube. This account includes 
an accurate description of the hippocrepian lophopliore, the 
number of tentacles being given as about sixty ; of the 
descending oesophagus and the ascending rectum, the position 
of the mouth, epistome, and anus being well described ; of 
the blood, containing red corpuscles ; and of the principal 
vessels, including the afferent and efferent trunks, the 
tentacular vessels, and some of the lophophoral vessels. 
The structure of P. oval is is described in less detail, but 
stress is laid on the form of its lophophore, which is oval but 
slightly flattened on one side. The tentacles were eighteen 
in number, and the blood-corpuscles were noticed. -The 
entire animal was about half an inch in length, and the gullet 
terminated in a globular gizzard, which communicated with a 
thick-walled stomach. Good figures are given of the oral 
ends of both species, the body of P. ovalis being figured as 
protruding from a delicate tube, embedded in the substance 
of the oyster-shell. The examination of Strethill W right's 
figures and description leaves no doubt that the specimens 
described in the present paper belong to P. ovalis. 
Although the eroded appearance of the outer surface of 
the Nept unea-shell furnished the clue which led to the 
discovery of the Phoronis, it does not appear to have been 
caused by the presence of this animal. The outer layers of 
the shell, both on the outer and on the inner side, are traversed 
by a number of branching’ hypha-like threads, which reach a 
diameter of as much as 24 /u ; and it appears probable that 
these are the principal cause of the erosion noticed on the 
outer surface. This is in accordance with the statements of 
Bornet and Flahault (1889), who give an account of various 
Algae and Fungi which bore in the shells of Molluscs. 
According to these authors the organisms in cpiestion 
commence their work by extending horizontally in the 
epidermic layer of the shell, subsequently sending branches 
vertically into the shell-substance and others parallel with 
the first set. These become so numerous and their branches 
