186 THE APODOUS HOLOTHURIANS 



ALCOOKI. 



Gepkyrothuria alcoclci Koehler and Vaney, 1905, p. 79 ; pi. v, figs. 6-8. 



LENGTH. Up to 50 mm., with a diameter of 17. 



COLOR. Eosy. 



DISTRIBUTION. Beported only from "Investigator" Station 278, near Cey- 

 lon, 3,442 m. (Koehler and Vaney). 



EEMARKS. The larger size and brighter color distinguish this from the 

 similar species of the American coast, aside from the generic differences 

 already discussed. The tentacles were so much contracted that it could not be 

 decided satisfactorily what the number of digits is. 



CONCLUDING EEMAEKS ON THE MOLPADIIDJE. 



INTERRELATIONSHIPS. 



Having thus characterized the 8 genera and 46 species of Molpadiidae 

 known to science at the present day, it may be worth while to attempt to show 

 in graphic form the relationship which they have to each other. There is good 

 reason for believing that the ancestor of the group was a 15-tentacled pedate 

 liolothurian, probably one of the Cucumariida?, or at any rate most nearly re- 

 lated to that family. Beyond this point our arrangement of the genera is 

 largely a matter of personal opinion ; but there will probably be general agree- 

 ment that Himasthlephora is nearest to such an ancestral form, because of its 

 still possessing rudiments of pedicels, as well as dorsal papillae, and its lack of 

 tentacle ampullae; Gephyrothuria is of course very little further removed. But 

 the absence of calcareous deposits in the skin and of posterior prolongations to 

 the radial pieces of the calcareous ring in these genera are probably not ances- 

 tral, but are more recent modifications. We may rank Acaudina next because 

 of the shape of the body, and follow with Caudina, the species with long and 

 distinct tails being farthest from the original form. It is natural to consider 

 Aphelodactyla as a modified Caudina, but it is probably just as near to Acau- 

 dina. The connection between Caudina and Molpadia is obvious and the divid- 

 ing line is hard to draw, while Ceraplectana is apparently a striking modifica- 

 tion of the latter. As for Eupyrgus, there is room for wide difference of opin- 

 ion, but it is apparently a much modified genus, which may have had a differ- 

 ent origin from the rest of the family, or may have been derived from a form 

 near Gephyrothuria. Assuming that the latter has been the more probable 

 course of development, the relationships of the genera might then be repre- 

 sented as follows : 



