THE APODOUS HOLOTHTJRIANS 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 dii¥erent 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 boiv; 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 Synaptin^. 



4. — Calcareous particles jjreseiit 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 iv, 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. 2-±). 



EUAPTA 



Calcareous ring with conspicuous anterior projections; stone-canals 

 numerous; anchor-plates aliruptly contracted posteriorly, and thus 

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



Opheodesoma 

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

 IV, fig. IT). 



D. — Tentacles numerous, normally 25 Polyplectana 



PD. — Tentfcles normally 15 or fewer. 



Sis:e very large; anchor-plates subrectangular or irregular, wqtli 



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) Synaptula 



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

 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 



C(7._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. 

 5.— Tentacles 12, with digits. 



Tentacles pinnate, with 5-13 digits Anapta 



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



BB. —Teniades 10, without digits Ehabdomolgus 



