TETRAXONIDA 275 



A comparison between A. carduus and A. glacialis 

 On comparing the types of Gellhis carduus, G. cardials, var. magellanica, G. laeris, 

 G. glacialis and G. glacialis, var. nivea, I find that there is no real difference between 

 them in external form or in the structure of the skeleton. The only distinction that can 

 be made rests on the differences in the dimensions of the spicules, especially of the 

 microscleres. I have already suggested that this group of three species and two varieties 

 represents no more than two species, so that the differences between these two species 

 may be expressed in the following way : 



G. carduus: Oxea o-49-o-6 mm. long; sigmata 0-02 mm. chord. 

 G. glacialis: Oxea o-53-o-65 mm. long; sigmata up to 0-145 mm. chord. 

 It is evident from the examination of specimens which have come to hand since these 

 species were first described that the sigmata in G. glacialis rarely measure so much as 

 0-145 mm. Sigmata are always present measuring 0-02 mm. and, in addition, larger 

 sigmata measuring o-o6, 0-07, o-o8, up to 0-12 mm. or so. Further, the larger and 

 smaller sigmata are not differentiated into two distinct categories, but are connected by 

 numerous forms intermediate in size. I suspect therefore that the species called here 

 Adocia carduus is merely a form oi A. glacialis in which the larger sigmata have dropped 

 out. It may be necessary to regard them ultimately as conspecific, but I would like to 

 have more material for examination before taking this step. 



There is, however, another point to be noted : that in the present collection there is 

 nearly a score of specimens from Sts. 160 and 177 which have the same general ap- 

 pearance as A. carduus and A. glacialis, the same arrangement of the skeleton, and the 

 same type of megascleres (i.e. oxea varying from abruptly pointed to sub-strong>-lote). 

 All these specimens are clearly conspecific and obviously belong either to A. carduus or 

 to A. glacialis, but to which it is quite impossible to say since none of them possesses 

 a single microsclere. It seems to me therefore that in this group of specimens from 

 Sts. 160 and 177, we have a number of individuals in which the reduction of the 

 microscleres, believed to have taken place in A. carduus, has been taken a step further 

 by the complete suppression of all microscleres. 



Adocia siphonella (Thiele). 



Reniera siphonella, Thiele, 1905, p. 460, figs. 75, 97-99. 



Occurrence. St. 6: Tristan da Cunha, 80-140 m. 



Remarks. The spicules in this specimen are usually strongyla, with a few oxea, 

 measuring 0-32 by 0-018 mm. Only a few fragments are to hand, but from these it 

 appears that, if my identification is correct, the species belongs to Adocia. Through the 

 kindness of Dr Arndt, of the Berlin Museum, I have been able to compare the present 

 specimen with one of the types, but as this also is in a fragmentary condition it does not 

 help in determining the generic position of the species. 



Distribution. Calbuco, Chile. 



