ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



551 



have arisen separately, and it seems probable that the former were the 

 first to leave the early Penasid stem. The Stenopidea may be included 

 along with the sub-order Natantia, i.e. as a tribe along with the tribe of 

 Penffiids, and the tribe of Carides. Within the Reptantia, the Brachym-a 

 and the Anomura stand out as natural groups. The Scyllaridea and 

 Eryonidea may be classed as a single tribe of the Eeptantia under the 

 title Palinura, and the other division, that of the Nephropsidea, may be 

 called Astacura. Thus the old Macrura are completely dispersed. A 

 tree is given showing the general relationships. The possible evolution 

 of the Caridea is also shown, and the author gives a very useful 

 diagnostic key to the classification of all the Decapods. 



Brachyura Anomura 



I I 



Palinura 



Astacura 



Penseids 



Caridea 



Stenopidea 



Geographical Distribution of Crayfish.* — E. A. Andrews suggests 

 a means of throwing light on the causes controlling the present distribu- 

 tion of crayfishes in North America. As is well known, on the west 

 side of the Rocky Mountains all the crayfish belong to the genus AstaciiSy 

 whilst elsewhere they are almost all of the peculiarly American genus 

 Camharus. As a contribution towards settling the question whether the 

 conditions in the regions occupied by Cambarus are unfavourable to 

 Astacus, he has transported females with eggs from Oregon to Maryland 

 and successfully reared young in captivity to a size of 60 mm. Whether 

 this species of Astacus can be introduced into eastern waters to compete 

 with Camharus, or to occupy regions free from Cambarus and to persist 

 as a permanent addition to the fauna, remains for more extensive 

 experiments to decide. 



Autotomy of Crabs. f — H. Pieron finds that in Grapsus varius a 

 gentle touch is sufficient to induce autotomy, and that as many as seven 

 of the walking appendages may be thrown off in succession, but never 

 more. The other three remain on, even though they be injured. 

 Autotomy occurs also when the crabs are suspended, but in cases of 



* Johns Hopkins Univ. Circular, n.s. No. 5 (1906) pp. 418-21. 

 t C.R. Soc. Biol. Paris, Ixii. (1907) pp. 863-4. 



