a single colony, too much stress cannot lx; laid u]K)n the bucls, the number of which inay 

 depend on the season of the year or on the condition of sexual maturity of the zooids. 



The descriplions of C. dodccalopJms which have previously been published were drawn 

 u]) in the absence of all Information relating to other species of the genus; and until this 

 information was forthcoming it was of course impossible to decide which of the characters were 

 of specific rather than of generic value. It may, however, be remarked that the specific name 

 given by M'Intosii proves to have been well chosen ; since, as I believe, the number of arms 

 is a character of specific value. 



The systematic position which Ccplialodiscns and Rhabdopleiira appear to occupy is 

 indicated by the following classification. 



HEMICHORDATA ')• 



Bateson (Quart. J. Alicr. Sci. XXV, Suppl., 1885, p. iii). 



Order i. ENTEROPNEUSTA Gegenbaur. 



Order 2. PTEROBRANCHIA Lankester. 

 (Quart. J. Mier. Sci. XVII, 1877, p. 448). 



= ASPIDOPHORA Allman. 

 (J. Linn. Soc. Zool. XIV, 1879, pp. 490 n., 586). 



= BRACHYSCOLECIDA BRANCHIATA Ehlers (90, p. 173). 

 = CEPHALODISCIDA + RHABDOPLEURIDA Fowler (92, 2). 



Fam. I. Cephalodiscidae. 



=: Enteropneusta Monobranchi.\ta Schimkéwitsch (93, p. 238). 



Cephalodiscus M'Intosh (82). 



Fam. 2. Rhabdopleuridae. 

 Rhabdopleura Allman. 



(Quart. J. Alicr. Sci., IX, 1869, p. 57; Rep. Brit. Ass. (1868) 1869, p. 311). 



? Order 3. PHORONIDEA. 

 Phoronis Str. Wright. 



l) Numerous other names, such as Pharyngopneusta, Archicoelomata, ïrimetamera, Archichorda, Diplochorda, Protochordata, 

 Adelochordata, "Uixhordaten", "Axobranclies", "Veimidiens", "Procordés", Braachiotrema, Hydvotrema, have been used as the equivalent 

 of Hemichordata, or of this group in addition to ethers, or of its subdivisions. These terms are for the most part dealt with historically 

 by DE Selys Longchami's (04, pp. 102 f.). Reference may also be made to Delage and Hérouard (97, 98) and to Willey (99). 



