238 
Gen. Diadumene Stephenson. 
Di agn osi s. Pedal disc well developed. Column smooth (or 
with suckers!). Cinclides scattered. A ring-like convex collar pre¬ 
sent round upper part of the column (always?). Margin not distinet. 
No differentiated sphineter. Tentacles numerous. Oral disc with 
tendency to be undulated. 6 or some more perfeet pairs of mesent- 
eries. Longitudinal muscle pennons diffuse or with tendency to be 
circumscript. Reproductive organs on the perfeet mesenteries ind. 
the directives and on the stronger imperfeet. Nematocysts of the 
acontia well developed (in the type specimen?). 
As before mentioned I have enclosed Åiptasiomorpha in the 
genus Diadumene (compare p. 234). Of the species of Åiptasio¬ 
morpha, set down in the paper of Stephenson (1920, p. 531), 
Å. minima is here described as a Diadumene and Å.diaphana, which 
is provided with a mesogloeal sphineter, belongs to the genus Ai- 
ptasia. Concerning Åiptasiomorpha paxi and leiodactyla a renewed 
examination of the sphineter is necessary, as it was probably over¬ 
looked by Pax. It ought namely to be remarked that this author 
has not observed the mesogloeal sphineter in tagetes and annulata. 
As to Stephenson’s division of the mesenteries into macro- 
enemes and microenemes in the type species of Diadumene I have 
already (p. 225) expressed my doubt. Also the constancy of the 
presence of a collar in all stages of expansion of the column is 
somewhat dubious. Annandale (1915, p. 77) says namely that 
if the column is fully expanded “the oral disc is withdrawn for 
some distance into the column and the wall of the latter are par¬ 
tially closed by a constriction above the tips of the tentacles“, and 
further “When the oral disc has been completely extruded the 
column itself contracts strongly“ because of a contraction of the 
longitudinal muscles in the mesenteries. In this stage “a very distinet 
fold “(collar)“ of the body-wall can be seen some little distance below 
the base of the tentacles". Whether the collar is visible also when 
the uppermost part of the column is expanded I find not mentioned 
in Annandale’s paper. Besides, it is remarkable that a collar- 
like formation is perspieuous in Åiptasia diaphana and Å. tagetes 
in certain stages of preservation. 1 have, however, provisionally 
put down the presence of a collar in the diagnosis. Concerning at 
