CLASSiriCATIO^f OP THK TUI^-ICATA. 619 



Ascicliozooids elongated, more or less distinctly divided into 

 three regions. Branchial aperture G-lobed ; atrial aperture pro- 

 vided with a languet. 



Test gelatinous or cartilaginous, sometimes incrusted with sand. 



Branchial sac large and well developed. 



Alimentary canal usually long and complicated, often twisted. 

 Stomach smooth-walled. 



Postahdomen separated from the abdomen by a constriction, 

 often projecting from one side of the intestinal loop. 



Some of the older described species of PohjcUnum are so im- 

 perfectly known that the following table cannot be regarded as 

 quite satisfactory, but it may be of use in roughly distinguishing 

 the species * : — • 



/Colony incrusted with sand 1 



[ Colony not sandy 2 



{Not very much sand in test, stigmata small. 

 P. molle, Herdm. (S. Atl.) 

 A good deal of sand in test, stigmata long and narrow. 

 P.fuiigosum, Herdm. (Austr.) 

 {Postabdomen attached to ventral edge of abdomen. 

 P. dcpressum, Herdm. (Austr.) 

 Postabdomen attached to posterior end of abdomen 3 



o f Colony of a greenish colour 4 



\ Colour not gi-een, generally grey or violet 5 



^/Gelatinous, green P. viride,D. Ch. (Med.) 



[ Not gelatinous, olive-green P. fens, Sav. (N.W. Eur.,?]VIed.) 



r Abdomen separated from thorax by a very long pedicle, as long as 



oj abdomen P. uranium, Hay. (Red S.) 



[ Abdomen separated only by a short pedicle 6 



P r Of a whitish or grey colour 7 



[ Of a violet or purple tint 8 



- r Colour whitish P. stdlatum, D. Ch. (Med.) 



I Colour grey P. vesiculositm, D. Ch. (Med.) 



g fOf a purple colour P. septosum, D. Ch. (Med.) 



I Of a bluish or violet tint 9 



q f With about 18 rows of stigmata ... P. hesperium, Sav. (Red S.) 



\ With 14-16 rows of stigmata 10 



r Abdomen nearly as large as thorax, stigmata small. 

 10 \ P. isiacum, Sav. (Red S.) 



[ Abdomen much smaller than thorax, stigmata large 11 



-,-, /With 14 rows of stigmata P. conddlatum, Sav. (Ind. O.) 



/With 15-16 rows of stigmata 12 



-,<;)/ Colour dark \iolet P. sfli'z(r«mM, Sav. (EpdS.,Med.) 



I Colour light violet P. cythereum, Sav. (Red S.) 



* Polyclinum diazona, D. Ch. (Med.), certainly does not belong to this genus — 

 probably not to the family. P. fiiscum, D. Ch. (Med.), has the branchial 

 aperture 8-lobed, and therefore cannot be a Polijclinum. 



