118 



TAi'.H SKOGSBERG 



drawn out into very long spine-like processes situated in the same din^etion as the lonpitiidinal 

 axis of the body; see the aeeompunying fig. X\'ll. 



In some species, e. g. Conchoecia imhricata (G. S. Hu.\il^) and C. symmetrica 

 Ci. W. Mt'LLER (see fig. 1 of the latter species in the special part of this work) tlie rostrum 

 is well developed and the posterior dorsal corner of both the right and the left valve is 



Fig. XVII. — The shell of Conchoecia caudala G. W. Mult.er. $, sppii from Ihr side. (From G. \V. Miii,i,F,R, 1906a.) 



hat is the relation 

 the shape of the 

 ?ll to the principles 

 lentioned above? 



furnished with a spine-like process situated in the same direction as the longitudinal axis 

 of the body but considerably shorter than in C. caudata; in addition some of these species 

 have weak processes, pointing about in the same direction as the first-mentioned processes 

 and corresponding to the mucrones in a number of Cladncera. The characteristic feature of 

 all the processes so far mentioned is consequently that they point in the same direc.tion as 

 the longitudinal axis of the body. In others the shoulder ridges on the shell are differentiated 

 as more or less powerful wing-like processes; these are found, for instance, in Conchoecia 

 alata G. W. MCller and Halocypris cornuta G. W. MUller (see G. W.MtJLLER, 1906a, pi. XXIX, 

 figs. 1 and 2 and pi. VIII, figs. 1 and 3). 



Only in one species (Thaumatocypris echinata G. W. MOller) do we find on the shell 

 a number of spines pointing in different directions; see the accompanying fig. XVIII. 



^ What view are we to take of these pro- 

 cesses and spines? 



The only writer who has touched on this 

 question is A. Steuer. In tliis author's work 

 of 1910 they are denoted (p. 208) as buoyancy 

 organs. It will soon, however, be obvious to 

 anyone who studies these matters in detail 

 that this explanation cannot be an adequate 

 one. If we look, for instance, at the posterior 

 part of the shell in Conchoecia daphnoides, we 

 shall see that this is rather decidedly flattened 

 at the sides, i. e. its horizontal section is rather 

 slight. That the two pairs of spines in the 

 genus Thaumatocypris cannot be explained as 

 adaptations of buoyancy is shown quite clearly 



Fig. XVIII. — The shell of Thaumatocypris echinata by their position, as they are not, as one would 

 G. U. ILiJLLF.R, juv., seen from the side. " . 



(From G. w. moller, 1906a.) expect according to the buoyancy theory, both 



