156 the apodous holothukians 



Key to the Geneea of MolpadiidzE. 



A. — Body surface witli no appendages whatever; skin iisnalh' with either calcareous or phos- 

 phatic deposits, or both ; calcareous ring usually with posterior prolongations ; teutacles 

 usually with ampulls. 

 i\— Tentacles 15, soft. 



C'.— Tentacles with 3-7 digits. 



I>. — Posterior end of body tapering, usually with a more or less conspicuous 

 caudal appendage; calcareous particles various. 



Tentacles with 3-7 short, blunt digits, counting the distinct terminal 

 portion (plate xi, fig. 1) ; caudal appendage (plate xiii, fig. 14) 

 usually less (sometimes more) than one-third of total length, some- 

 times not distinctly set off from body, which generally' has colored 



phosphatic deposits in skin Molpadia 



Tentacles with 2 pairs of rather long, pointed digits (plate x, fig. 2) ; 

 terminal digit practically wanting; caudal appendage (plate ix, figs. 

 1, 6, and 9) one-third or more of total length, usually abruptly dis- 

 tinct from body, which very rarely has colored phosphatic deposits 



in skin Caudina 



DP. — Posterior end of body blunt and rounded, without a trace of a caudal ap- 

 pendage ; calcareous particles, thick plates with a few sharp projections 



and small perforations Acaudina 



CC. — Tentacles simple, without digits (plate xii. fig. 23). 



Tentacles without ampullfe ; radial pieces of calcareous ring, without posterior 



prolongations ; size very small, under 25 mm Eupyrgus 



Tentacles with ampulla; ; radial pieces of calcareous ring with posterior pro- 

 longations; size large, 40-200 mm Aphelodactyla 



BB. — Tentacles 10, horny and undivided (plate xiii, fig. 6) Cer.vplectana 



AA. — Body surface with a few whiplash-like appendages in mid-dorsal interambulacrum : no 

 calcareous or phosphatic deposits ; calcareous ring with no posterior prolongations ; ten- 

 tacles without ampulla?. 



Caudal appendage long and slender; tentacles with 4 digits Himasthlephora 



No caudal appendage (or perhaps a rudimentary one) ; tentacles with only 2 digits. 



Gephyrothdria 

 MOLPADIA Cuvier, 1817. 



naplodadyla Grube, 1840 (non Semper). 

 Liosoma Stimpson, 1857 (non Brandt). 

 Embolus Selenka, 1867. 

 Trochostoma Danielssen and Koren, 1877. 

 Ankyroderma Danielssen and Koren, 1879. 



Tentacles 15, with one, sometimes two, rarely three, pairs of digits and a 

 terminal digit which is commonly the largest of all. Body rather stout, 

 usually with a distinct but short caudal portion, which is generally much less 

 than one-third of the total length. Radial ]neces of calcareous ring with con- 

 spicuous bifurcate posterior prolongations. Calcareous deposits in the form of 

 tables, often very imperfect; perforated plates, and more or less fusiform rods. 

 In many cases anchors are also present in connection with either a single irreg- 

 ular plate or a gi'oup of 2-8 plates, which are often racquet-shaped and form 



