488 GEOLOGICAL SURVEY OF THE TEERITORIES. 



of the water, at which it (the variety a.) forms the transition to the cor- 

 responding variety of A. milhausenii, that is, at 15°, 1G°, and 18° con- 

 centration after Beauui(3's instrument. In concluding, it results that at 

 such a concentration of the salt water, at which the above stated meas- 

 urements of A. salina showed themselves, i. e., at 9° Beaume, and the 

 temperature of the month of September, we must obtain the following 

 figures for this race : 



The gill-sacs The posterior branchial lobes 



must amount in their length 

 the 25th, . the 16, 5th, 



in their width 



the 52d the 34th 



part of the whole body-length. 



The variety Branchipus ferox, hereabouts living in salt water ditches, 

 and to which is peculiar a lesser concentration of the salt water, how- 

 ever at a higher temperature than that peculiar to the species Branchipus 

 s2nnosus, yields the following figures, in relation to the gill-sacs and 

 posterior branchial lobes : 



The gill- sacs The posterior branchial lobes 



amount in length to 

 the 24th, the 20th, 



in width 



the 5Cth the 43d 



-part of the whole body-length. 



The variety BranoM/pus ferox (from salt-water ditches) is, in its leg- 

 ai)pendages and according to the element which it inhabits, in propor- 

 tion to Artemia salina as Branchipus spinosus is to varietas a. of A. salina. 

 Especially those generations of A. salina which live in salt-water ditches 

 of about 4° Beaume, or the generations of the second variety of A. sa- 

 lina (varietas b.) are in relation to gill-sacs and posterior branchial lobes 

 and some other characters, also in the element in which they live nearer 

 the salt-lake generations (from salt-water ditches) of Branchipus ferox 

 (varietas). I must add here that the legs themselves are longer in 

 Branchipus ferox var. and in A. salina than in Branchipus spinosus and 

 in A. salina varietas a., and that only on this account the posterior 

 branchial lobes of the forms of the one or the other category relative to 

 length have no great diiferences. But the length of the legs corre- 

 sponds with that temperature and with that concentration of the salt 

 water which is peculiar to each of these forms.^ 



Ooncerning Branchipus medius mihi, we can nevertheless recognize 

 abstractedly from the point that it forms a too isolated species in its 

 characters and in the relation-figures of its gill-sacs and posterior bran- 

 chial lobes, the result of the effect of the element in which it is dis- 

 tributed, as 1 have mentioned in the description of this species.^ 



The knowledge of the effoct of the surrounding element uj^on the gill- 

 sacs and the posterior branchial lobes in these animals is important 

 because the differences of size between these appendages, according 

 to authors (Milne-Edwards, S. Fischer, Grube), represent no important 

 species-characters. 



It is here the place to add a few remarks which show how far the 

 life of A. salina depends on the air-capacity (actually the oxygen of the 



1 Consult any paper in tlio *'Schriften der Neurussiaclien Gesellschaft der Natur- 

 forscher," 1875, vol. iii, 2d part, pp. 297 to COO. 

 ^Ibidtm, pp. 305 to 313 



