70 THE APODOUS HOLOTHURIANS 



sels and stone-canals, the form of the ciliated funnels, the arrangement of the 

 alimentary canal and its mesemaries, the form of the longitudinal muscles (in- 

 cluding the presence of so-called "retractors"), and the appearance of the re- 

 productive organs are all characters which are subject to much individual di- 

 versity, often according to age, time of year, size, and habitat, and little 

 weight can be placed on them in distinguishing species. Of characters for 

 distinguishing genera, aside from the calcareous particles, the number and 

 the form of the tentacles are the best, and while others may occasionally be 

 used, no great weight attaches to them. The genera used in this report are 

 easily recognizable (except that Molpadia and Caudina are not always distinct 

 from each other), and there need be no difficulty in distinguishing them. Un- 

 fortunately the same cannot be said for the species. Many of the latter are 

 very closely related, but still apparently distinguishable, and must be retained 

 for the present, while others are almost certainly based on abnormal or im- 

 mature individuals. In other cases it is quite possible that two or more species 

 are included under a single name. No doubt the present compiler has made 

 errors in many cases, but it is hoped that in spite of these the classification 

 here offered may prove satisfactory to students of the Synaptidae, and may 

 be the basis for much further investigation of the taxology of the group. 



KEY TO THE SUBFAMILIES OF SYNAPTIOE. 



A. No wheels, sigmoid or bracket-shaped particles present in the skin, but usually anchors 

 and perforated plates ; deposits rarely wholly wanting ; tentacles never peltato-digitate. 



A. A. Wheels, sigmoid or bracket-shaped particles commonly present in the skin, but no 

 anchors; deposits sometimes wholly wanting; tentacles commonly peltato-digitate. 

 Wheels present or wanting; if present, never with more than six spokes. 



CHIRIDOTIN^J 

 Wheels present, with eight or more spokes .................... MYRIOTROCHIN^E 



SYNAPTINJ3 Ostergren, 1898&. 



Tentacles with the stalk cylindrical or terete, not becoming widened dis- 

 tally, either with digits along each side for most of its length (pinnate) or with 

 only one or two digits on each side near the tip (digitate) or without digits 

 at all (simple). Calcareous deposits, usually anchors and perforated plates, 

 often accompanied by irregular, curved rods or minute particles (miliary 

 granules), but any or all of these may be wanting. Hermaphroditic so far as 

 known, except possibly Ehabdomolgus. 



In the following keys and descriptions the terms which are used are com- 

 monly self-explanatory, but some explanation is needed of those used in 

 reference to the calcareous particles. The term miliary granules does not 

 include any particles occurring in the tentacles or in the longitudinal 

 muscles, so that a species in which it is stated that the "miliary granules 



