408 Dr. W. G. Ridewood— .4 Key for the Recvly 



words, tlie synopsis itself should he consuhed hy those wishing 

 to discrimiuate between these species. As regards the two 

 diminutive species of tlie subgenus Deviiothecia, Iliinnev 

 writes (' Pterobranchia of the " Siboga " Expedition of 1809- 

 1900,' Leiden, 1905, p. 4) : — " The possibility is not excluded 

 that C. sibogcc is the male form of C. gracilis." 



A study of the large ami varied collection of C. devsms 

 obtained by the ' Terra Nova ' leads to the conclusion that 

 what Andersson described as C. varus is but an early colony 

 of C. densus, with the tubes of the coenoecium lax, straggling, 

 and irregular, instead of closely set and more or less parallel 

 — see ' Terra Nova ' Report, pp. 39-40. 



Gravier's species — C anderssom — is with difficulty distin- 

 guishable from C. densus ; his description of the zooids is 

 incomplete, and the principal feature that distinguishes the 

 ccenoecium of his species is the aggregation of the tubes into 

 clumps or clusters which stand out more or less distinctly 

 from the other clumps — see 'Terra Nova' Report, pp. 40 

 and 76. 



Tlie present key is so drawn up as to bring the species 

 iiigrescens and sofidus together. Although belonging to 

 different subgenera, tliey have many points in common, antl 

 I was for some time uncertain whether the cone-shaped 

 colonies obtained on the Australasian Antarctic Expedition 

 of 1911-1914 were small, short-tubed colonies of C.soUdiis or 

 unbianched colonies of C. niyresceus — see report on the 

 Pterobranchia of the expedition, Sydney, 1918, pp. 19-20. 

 The arms of well-preserved zooids of C. niyresceus show a 

 characteristic double black band on the axis, but the bands 

 are lost in badly preserved material. On the other hand, 

 it is not definitely known that the zooids of C. solidus do not 

 possess such bands ; Andersson does not mention them, and 

 the zooids of one of his specimens that I had an opportunity 

 of studying do not show tiiem ; the material, however, is not 

 well {(reserved, and there are evident signs of the colour of 

 the zooids having become diffused and reduced in intensity. 



The key is also arranged so as to bring together the two 

 specially arenaceous species ayglutinans and ecctusi ; the 

 tbrmer has black zooids and the latter white. Although 

 C. ayglutinans differs from the other s[)ecies of Idiuthecia in 

 the tubes n()t emling blindly in the middle of the branch, the 

 character is not readily determined, o\\ ing to the transj)aroncy 

 ami thinness of the tubes ami the contusing etfect of the 

 numerous particles of shell embedded in the cocnoccial 

 substance. 



