TWO NEW TYPES OF ACTTNIARTA. 
151 
stout plate, club-shaped in transverse section, and carrying 
large muscle-fibres (fig. 15). To this, but marked off from it 
by a sudden change in the thickness of the lamina, is attached 
the contorted region of the mesentery, provided with more 
muscle than is generally the case. 
The muscle of the body wall and oral disc is endodermal 
and circular, and is not differentiated into a sphincter at any 
point. 
As is so often the case, nematocysts of two kinds were 
present, of which the larger measured as much as ‘14 mm. x 
•044 mm., and were provided with unusually large cnidocils. 
In conclusion, I desire to express my thanks to Mr. John 
Murray, by whose courtesy I am permitted to present an 
account of these two interesting forms. 
Since writing the above description, I have had the great 
advantage of submitting my drawings to Professor ft. Hertwig, 
who inclines to the opinion that Phialactis should be asso- 
ciated with the Corallimorphidm. While it is probable that a 
parallel retrogression of the tentacles has taken place in more 
than one family simultaneously, it will perhaps be best, till 
the steps in the process are known, to allow the Phialactidse to 
stand near the Liponemidse, although the genera in both 
families may be eventually found to be merely degenerate 
representatives of other existing families. 
EXPLANATION OF PLATE XV, 
Illustrating Dr. G. Herbert Fowler’s paper on “Two New 
Types of Actiniaria.” 
Figs. 1 — 9. — Thaumactis medusoides, gen. sp. nn. 
Fig. 1. — The largest specimen, retracted ; from the oral aspect. While 
the rest of the polyp has been drawn by transmitted light, the pseudo- 
tentacles scattered over the surface are, for clearness’ sake, represented 
as if under reflected light. Compare with this fig. 3. The clear space 
