158 Happon anp DurrpEN—Some Actiniaria from Australha and other Districts. 
Endoderm regular ; well developed parieto-basilar muscles on each side. On 
the, side opposite to the retractor muscle is a special outgrowth of mesoglea 
(‘‘pennon”’) for the basal muscle of that side. Retractor muscles well developed 
on numerous deep plaitings of the mesoglea; those are often slightly complex. 
Mesoglcea fairly thick in muscular region. 
Mesenterial filaments well developed, with abundant narrow nematocysts. 
The mesenteries quite fill up the ccelenteron in the contracted spirit specimens. 
Gonads.—'T estes occurred in all three specimens. 
THAUMACTIS. 
Aliciidee with irregularly scattered, complex vesicles, which when fully 
developed are prolonged into an elongated tubular process. Tentacles marginal ; 
about twenty in number. Kctodermal muscle fibres in capitulum and cesophagus. 
Feeble, diffuse, endodermal sphincter. Two cycles of perfect mesenteries. No 
cesophageal groove. 
We have drawn up the foregoing diagnosis, from the description by Dr. G. H. 
Fowler, of Thaumactis medusoides,* gen. sp. nn. The specimens at Dr. Fowler’s 
disposal were very young, and strongly retracted forms. These circumstances, 
combined with the delicacy of the tissues and the flattening of the body, some- 
what misled that investigator. Thus he has mistaken the vesiculated column 
for an “oral surface” bearing irregularly scattered ‘‘ pseudo-tentacles.” His 
‘‘invaginated oral surface” is the capitulum. ‘The mesenteries are apparently 
arranged on the Hexactinian plan, the irregularity noted by Dr. Fowler being 
probably due to immaturity. His largest specimen had paired mesenteries in 
three cycles; but those of the third cycle were imperfect in the sulculo-lateral 
exoceel. In one specimen there was only one pair of directive mesenteries, and 
in another none were present. We do not regard the ectodermal muscle of the 
capitulum and cesophagus as being of sufficient importance to warrant the creation 
of a new family for its occurrence; and the presence of a general ectodermal 
muscle enters into the diagnosis of the tribe as given by Carlgren. 
From the foregoing description, it is evident that there is no need to place 
this form in a new tribe (Thaumactiniz). Dr. Carlgren suggests that it might be 
placed as the representative of a new family (Thaumactinide) among his Prot- 
antheee. 
We have retained Dr. Fowler’s genus on account of the formation of the 
vesicles and the ectodermal muscle. It is certainly a member of the family 
Alicudee. 
* «Two New Types of Actiniaria,” Quart. Journ. Micr. Sci., xxrx., 1889, p. 148. 
