234 
The shortest muscle folds in these latter are often situated in the 
middle part of the pennons. The parietobasilar muscles of the per- 
fect mesenteries are distinet but not strong. They are, however, 
by a fold inwards separated from the main lamella of the mesent¬ 
eries (textfig. 34). In the imperfeet mesenteries the parietobasilar 
muscles and the longitudinal muscles — both more strongly developed 
in their inner parts — form an almost continuous layer. The im¬ 
perfeet mesenteries of the second order have filaments. Also in 
some of those of the third order I have observed filaments. The 
acontia are well developed and contain numerous nematocysts 29 
— 41X2,5—well 4 ( 4 , 5 ) //. Possibly there are here two kinds of 
nematocysts, partly 29—31 X2,5, partly 34—41 X3—4 ( 4 , 5 ) f.v. The 
basal part to the spiral thread is mostly perspieuous in the former, 
indistinet in the latter. The reproductive organs were not devel¬ 
oped in the two examined specimens. 
Fam. Diadumenidae. 
Di agn osi s. Thenaria without sphineter. Column without 
ectodermal muscles. Margin not distinet. Tentacles not retractile or 
not perfeetly. Longitudinal muscles of tentacles and radial muscles 
of oral disc ectodermal. Mesenteries not or not distinetly divisible 
into macro- and microenemes. Muscle pennons diffuse or with a 
tendency to be circumscript. Reproductive organs from the mesent¬ 
eries of the first cycle.'Nematocysts of the acontia well developed 
(in the type-specimen of Diadumene?). 
The diagnosis of the family Diadumenidae is altered here, owing 
to the exeluding of all genera except Diadumene itself from the 
family (compare p. 224) and the enclosing of the genus Åiptasio- 
morpha in the genus Diadumene. I am namely of opinion that if 
we retain the family Diadumenidae we must transfer Åiptasiomorpha, 
distinguished from Åiptasia by the absence of a sphineter, to this 
family. On the other hånd it seems that Diadumenidae and Åip¬ 
tasia with its cognates are nearly related to each other, wherefore 
in the future it may possibly be necessary to place Diadumene in 
a family Aiptasiidae (as subfamily already proposed by Simon 
1892). The genus Åiptasia and its related forms, Bartholomea, Carl- 
greniella and Heteractis, are namely not so heterogeneous as shown 
in Stephenson’s diagnosis (1920), but are a very homogeneous 
