CKRIANTHARIA. 



43 



As is known (Busch 1851), the larval form of Ccrianthus mcmbranaccus appears not to have a 

 long period of development, but to sink quickly to the bottom. It may also be possible, therefore, that 

 the most larval forms of the Cerianthidae family are not planktonic for any long period, and that the 

 larval forms, which are more adapted for the planktonic mode of life, belong principally to the families 

 Acontiferidae and Botrncnidiferidae. 



Besides the generic characters given above, there are undoubtedly a number of others that 

 will prove to be of significance for the discrimination of genera. In the above however I have endeav- 

 oured to give the genera as extensive a range as possible in order not to run the risk of having 

 to suppress certain characters afterwards. However as these more secondary characters may be of use 

 for a future characterisation of the genera, they are stated here. 



Genus Pachycerianthus: Species as a rule with rather numerous mesenteries. Breadth of sipho- 

 noglyph and length of hyposulci vary. The median streak with a tendency at least to break up into 

 two streaks. The mesogloeal processes of the ciliated tracts issue from the main lamella of the 

 mesentery. Mesenterial threads (craspedonemes) and bunches of the ciliated tracts may or may not 

 be found. The region of the craspedion may or may not be found. The cnido-glandular tract on 

 mesenteries M and m sometimes threadlike, from its exterior suggestive of the "acontia" and of the 

 craspedonemes of the ciliated tract. 



Genus Ccrianthus: Species as a rule with numerous mesenteries. Siphonoglyph narrow. Hypo- 

 sulcus as a rule small. The median streak and mesogloeal processes of the ciliated tracts as with 

 Pachycerianthus. Mesenterial threads (craspedonemes) and bunches in the region of the ciliated tracts 

 may or may not be found. The region of the craspedion may or may not be found. 



Genus Ccriantheopsis: Species with numerous mesenteries. Siphonoglyph narrow. Hyposulcus 

 small. Median streak with marked tendency to divide into two lateral portions. The mesogloeal 

 processes of the ciliated tracts issue from the main lamella of the mesentery. Craspedonemes and 

 bunches in the region of the ciliated tracts occur. The region of the craspedion is present, long. Proto- 

 cnemes 2 and the longest metacnemes with a craspedoneme from the most aboral part of the region 

 of the craspedion. 



Genus Arachnanttnis: Species with a small number of mesenteries. The 2nd couple of proto- 

 cnemes without cnido-glandular tract region. Number of metamesenteries not large. Very broad si- 

 phonoglyph and long hyposulcus. With distinct filament region on hyposulcus. Median streak divided 

 up into 2 streaks sharply marked off. The mesogloeal processes that support the ciliated tracts issue 

 from the mesogloeal folds of the median streak. The region of the craspedia on M and m well 

 developed. Without mesenterial threads (craspedonemes) and bunches in the region of the ciliated tracts. 



Genus Botrucnidifer : Species with a small number of mesenteries. Siphonoglyph narrow, feeble 

 hyposulcus. Median streak simple, not subdivided. The mesogloeal processes of the ciliated tracts 

 issue from the main lamella of the mesentery. Long craspedion region. Mesenterial threads (craspe- 

 douemes) and bunches in the region of the ciliated tracts not developed. 



Genus Botruanthus: Species with very numerous mesenteries. Siphonoglyph very broad. Hypo- 

 sulcus of medium development Conformation of the median streak? Mesenterial threads (craspe- 

 donemes) occur. Craspedion region? 



6' 



