164 SPOLIA ZEYLANICA. 



The genus Holothuria, as it is at present understood, will 

 be composed of tliree sub-genera — (1) Bohadschia, to which 

 such a form as Holothuria marmorata belongs ; (2) Halodeima, 

 which will include Holothuria atra and its allies ; and (3) 

 Thymiosicya, of which Holothuria impatiens may be regarded 

 as the type. The genus Miilleria will be divided into two 

 sub-genera — (1) Actinopyga, including such forms as MuUeria 

 miliaris ; and (2) Argiodia, to which MuUeria maculata and 

 its allies belong. 



Diagrammatic ally the proposed changes may be represented 

 as follows : — 



Sub-genera : — 

 ( Bohadschia ^ 



Genus Holothuria J Halodeima i _, tt i i 



] rm. ■ ■ (j(en\i& Holothuria 



Thymiosicya > 



K, . ,. I sens. nov. 



Genus MuUeria j j^^^^^opyga | 



( Argiodia J 



There are only four characters of any taxonomic value in 

 the genus. These are (1) the arrangement of the ambulacral 

 appendages ; (2) the nature of the spicules ; (3) the presence 

 or absence of anal teeth; and (4) the structure of the calcareous 

 ring. The number and arrangement of the tentacles, Pohan 

 vesicles, and stone canals are variable characters even within 

 the limits of a single species. This is also true of the 

 Cuvierian organs. 



Ambulacral Appendages. 



The ambulacral appendages show considerable variation 

 within the genus both as regards the kinds of appendages and 

 also their distribution. 



It is difficult to say whether any members of the genus are 

 supplied with true pedicels only, although many authors have 

 described such species, and Ludwig gives this character m his 

 diagnosis of the genus Holothuria. Most workers at the 

 group have not examined Uving specimens of the forms they 



