ACTINIARIA 



189 



forms as Pycnanthus and possibly also in Parasicyonis (compare below) it is questionable, if the subfamily 

 Actinostolinae may be maintained. 



The exterior of the Paractiidae is rather uniform, especially that of the column which is smooth or 

 in a few forms tuberculated. Also the tentacles in the genera seem to agree well. They are commonly short, 

 smooth, or in contracted state wrinkled, or sometimes longitudinally sulcated. In several forms they are 

 more or less bulbous on the outside of the base as in Actinoscyphia, Pycnanthus lacvis, but not in P.densus 

 and maliformis, Sicyonis crassa, tuherculata and ingolfi (but not in S. variabilis), Ophiodiscus and some Acli- 

 nostola-species. As they sometimes appear only in certain species of a genus, their occurrence is rather in- 

 significant as a genus-character, even in certain cases as a species character; I have namely in Actinostola 

 callosa found all transitory stages between tentacles with bulbous thickenings [A. atrostoma) and tentacles 

 without such (compare A . callosa) . This variation of a species does, however, not prevent that the bulbous 

 thickenings may be more constant in other species or in certain genera. In the genera Anthosactis and Tea- 

 lidium we meet with a special differentiation of the tentacles. At the sometimes thickened base of the outside 

 of the outer tentacles there is a well developed stinging batterj^, containing large, closely placed nematocysts 

 of a special appearance (compare these genera). Similar capsules, though considerably smaller, appear in 

 Actinostola and Stomphia, but are here arranged mainly in the apex of the tentacles. 



The tentacles are commonly hexamerously grouped, in Anthosactis fan mayeni octomerously. In 

 Stomphia the tentacles of the second cycle are twice the usual number or almost so, and the arrangement 

 6 + 12 + 18 etc. or 6 + 10 + 16 etc. Also in Sicyonis the tentacles are probably arranged in a similar 

 manner. In Actinoscyphia they are found close by the margin of the oral disc in only two cycles. Possibly 

 that is the case also in Epiparactis. In Polysiphonia the tentacles are placed in 12 triangular, continuous 

 groups with the largest tentacles, corresponding to the first and second cycles of endocoels, in the innermost 

 parts of the groups. 



The longitudinal muscles of the tentacles are wholly ectodermal in Actinoscyphia, Archactis (Antho- 

 loba?) pcrdix, Anthosactis ingolfi, Antiparactis, Epiparactis, "Paractis" ignota and ferax and Paranthus, ecto- 

 dermal to meso-ectodermal in Antholoba and Anthosactis fan mayeni, meso-ectodermal to ecto-mesogloeal ? 

 in Anthosactis (Alloactis) excavata, and mesogloeal in Actinostola, Aulorchis, Cymbactis, Hormosoma, Ophio- 

 discus, "Paractis" papaver and polaris, Parasicyonis, Pycnanthus, Polysiphonia, Sicyonis, Stomphia and 

 Synsicyonis. 



The genera and species, with the longitudinal muscles of the tentacles either ectodermal or mesogloeal, 

 have the radial muscles of the oral disc arranged in a similar way. In Antholoba and Archactis perdix they 

 are more enclosed in the mesogloea and thus ecto-mesogloeal, in Anthosactis fan mayeni meso-ectodermal 

 and in A. excavata ecto-mesogloeal. 



The siphonoglyphes are always present and well-developed. 



The mesenteries in most genera show a regular development and are commonly hexamerous, in 

 Anthosactis fan mayeni octamerous. Both mesenteries of the same pair are for the greater part equivalent; 

 in Actinostola, Stomphia, Sicyonis and perhaps also in some other genera they show a different development 

 of the younger cycles. In the latter case they follow the Actinostola-vnXe. Traces of such an arrangement 



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