THE APODOUS HOLOTHURIANS 71 



are wanting" may have supporting rods in the tentacles and small oval 

 bodies in the longitudinal muscles. When the miliary granules have a number 

 of short curved branches, they are called rosettes. The different parts of the 

 anchor are the arms and the shaft; the point where the arms meet and join the 

 shaft is the vertex, and this is the anterior end; at the opposite (posterior) end 

 of the shaft is the stock. The anchor-plate lies below the anchor, and the end 

 beneath the stock is of course the posterior end ; it is across this end that the 

 rod extends, which is called the bow; the anterior end is commonly the wider. 

 In the key to the genus Protankyra the term "accessory calcareous particles" 

 is used for any calcareous bodies in the skin (not in the tentacles) other than 

 the anchors and their plates. 



KEY TO THE GENERA OF STNAPTIN^. 



A. Calcareous particles present in form of anchors and anchor-plates. 



B. Arms of anchor smooth; vertex usually with minute knob-like projections (plate 

 iv, figs. 17, 25). 



C. Cartilaginous ring posterior to calcareous ring usually wanting; stock of 

 anchor branched irregularly (plate rv, fig. 25). 



Calcareous ring without noticeable anterior projections; stone-canals 

 not numerous; anchor-plates not abruptly contracted at posterior 

 end, but with a large, smooth hole on each side (plate iv, fig. 24). 



EUAPTA 



Calcareous ring with conspicuous anterior projections; stone-canals 

 numerous; anchor-plates abruptly contracted posteriorly, and thus 

 lacking a large, smooth hole on each side (plate v, fig. 24). 



OPHEODESOMA 



CO. Cartilaginous ring commonly present; stock of anchor not branched (plate 

 iv, fig. 17). 



D. Tentacles numerous, normally 25 POLYPLECTANA 



DD. Tent?cles normally 15 or fewer. 



Size very large; anchor-plates subrectangular or irregular, with 



numerous smooth holes (plate iv, fig. 19) SYNAPTA 



Size diverse ; anchor-plates rounded in front, narrow behind, with 

 few holes, the largest dentate and regularly arranged (plate vi, 



figs. 11, 12) SYNAPTDLA 



BB. Arms of anchor usually serrate, sometimes smooth; vertex without knobs (plate rv, 

 figs. 3, 8, 12, 15; plate v, figs. 1, 3, 5). 

 C. Tentacles pinnate, with 5-21 (usually more than 7) digits or simply pin- 



nately notched, without digits LEPTOSYNAPTA 



CO. Tentacles digitate with 3-5 digits. 



Anchor-plates abruptly narrowed into a sort of handle (plate v, fig. 23) 



LABIDOPLAX 

 Anchor-plates irregular with numerous holes, not narrowed into a handle 



(plate iv, figs. 4, 5, 9, 13) PROTANKYRA 



A A. Calcareous particles never in form of anchors or perforated plates. 

 B. Tentacles 12, with digits. 



Tentacles pinnate, with 5-13 digits ANAPTA 



Tentacles digitate, as in Protankyra, with only 4 digits DACTYLAPTA 



BB. Tentacles 10, without digits RHABDOMOLGUS 



