548 T. A. STEPHENSON 
macro- and microcnemes. 10, Numerous perfect mesenteries. 11. No 
acontia. 
THALASSIANTHIDAE. Genera: Thalassianthus, Crypto- 
dendron, Actineria. Common characters, 10. 
1. Definite base. 2. No vesicles. 3. Sphincter endodermal, not 
very strong, may be circumscribed. 4. Disc and tentacle radial 
muscle ectodermal. 5, Tentacles divided into dendrites and nemato- 
spheres. 6. Not more than one dendritic tentacle per exocoel, and 
no nematospheres. 7. Typically more than one dendrite, and nemato- 
spheres, on endocoels. 8. Mesenteries not divided into macro- and 
microcnemes. 9. Numerous mesenteries perfect. 10. No acontia. 
STOICHACTIDAR. Genera: Stoichactis, Radianthus, 
Antheopsis. Common characters, 11. 
1. Definite base. 2. No vesicles. 3. Sphincter endodermal, 
strong or not very strong, may be circumscribed. 4. Tentacular 
longitudinal muscle ectodermal. 5. Oral disc not produced into 
permanent arm-like lobes. 6. Tentacles simple, all of one sort (but 
for sporadic cleft ones which are sometimes present). 7. Not more 
than one tentacle per exocoel. 8. More than one tentacle on at least 
each older endocoel, except in very rare cases; usually some or all 
of the endocoels have several or many. 9. Mesenteries not divided 
into macro- and microcnemes. 10. Numerous perfect mesenteries. 
11. No acontia. 
HETERANTHIDAE. Genus: Heteranthus. Chief char- 
acters, 9. 
1. Definite base. 2. No vesicles. 3. Sphincter endodermal, not 
very strong, circumscribed. 4. Tentacles of two sorts, marginal! and 
discal. 5. Oral dise not produced into permanent arm-like lobes. 
6. Marginal tentacles short conical, disc-tentacles wart-like. 7. Mesen- 
teries not divided into macro- and microcnemes. 8. Numerous perfect 
mesenteries. 9. No acontia. 
The other ten families were listed and dealt with in Part I. 
It will be seen from an inspection of the above lists, that at 
the minimum each family has six common characters, and 
most have 7 to 11, a few even more. It must also be remem- 
bered that the lists are not exhaustive, and that most of them 
could be added to and even some of the characters subdivided. 
For instance, * presence of ciliated tracts on the mesenterial 
