HABIT AND HABITAT IN THE GALATHEIDEA. 95 



crab-like habit and sluggish nature of the species (compare the settlement 

 of Spirorbis, etc., on the carapace and chelae). 



In this last instance, then, P. platycheles exhibits a type of specializa- 

 tion markedly analogous with that of the true crabs, and the species once 

 more asserts its right to be placed among the upper branches of our tree 

 of G-alatheid ascent. 



EXPLANATION OF PLATES. 



Plate 1. 



A.-E : Thoracic nervous systems of Decapod Crustaceans. 



A. Of Astacus fluviatilis (after Huxley). 



B. Of GaJathea squamifera \ 



C. Of Munida rugosa > members of the Galatheidea. 



D. Of Porcellana platycheles ) 



E. Of Cancer pagurus. 



Gn. 1. = supra- cesophageal mass. 



C. ce. =circum-oesophageal ring. 



S. oe. =sub-oesophageal ganglion. 



S. n. — g^P foi^ sternal artery. 



Gn. 4, 5-8. =last 5 thoracic ganglia. 

 Gn. 8. = ganglion of segment XIII. 



Yn. = ventral nerve-mass. 



F and G. Branchial cavity of right side, showing bases of thoracic legs. 



A. Of G. squamifera. 



B. Of P. platycheles. 



PI. X to XIII = Pleurobranchia. 

 Ep. VIII to XI^Epipodites. 



Plate 2. 



A. Side view of carapace of Galathea strigosa. 



Ep. YIII=epipodite of the 3rd maxillipede (usually turned into the 

 branchial cavity). 



B. An epipodite of G. squamifera, showing sweeping hairs. 



Ms. = muscle. 

 D. P. pJatycheles, dorsal view. The flagellum of the left side is at work. 

 (N.B. — In this specimen, the chela of the right side is the larger. 

 The illustration by no means does justice to the general shagginess 

 of the species.) 



