224 Mr. C. Spence Bate on Synaxes. 



It must have been based almost, if not absolutely, on the 

 uniformly simple character of the pereiopoda, or walking-feet, 

 although Milne-Edwards supported it by the character of the 

 branchial appendages ; but the condition of depression that 

 he assigns to the Macro^ires cuirasses is scarcely in accordance 

 with the cylindrical form of Palmurus. But this advanced 

 carcinologist has separated them into distinct tribes (sub- 

 families), based on the very distinct form of their antennae ; 

 while Leach classed them in one family, which corresponds 

 with Macroures cuirasses of Edwards, except that he included 

 the geuus Porcellana as well as Galathea ; while Edwards 

 includes Galathea and the Eryonidffi, which latter family was 

 not known to Leach, and only to Edwards in a fossil con- 

 dition. 



The union of these very distinct generic forms, in some parts 

 so wholly unlike, clearly demonstrates that the conclusions 

 that have been arrived at were based on a hypothetical rather 

 than on a clear appreciation of the structure and development 

 of the several genera. 



If we take the carapace of the two forms and place them 

 side by side, without any of the appendages attached, we 

 shall at once see how very distinct that of Ibaccus and all the 

 Scyllaridaa is from that of the Palinuridte, even when we 

 take them from Arctus^ the nearest approximating genus of the 

 two families. 



In the Scyllarida3 the eyes are implanted in two distinct 

 and perfect orbits that are almost complete in their circular 

 circumference ; and these are situated far apart, in some genera 

 (as Scyllarus) as far as the limits of the carapace will admit. 



In the Palinuridte there is no orbit, and the peduncular 

 structure, whether calcareous, as in Palinurus, or membra- 

 nous, as in PanuliruSj lies in front of the anterior margin of 

 the carapace, and the eye-peduncles are connected with each 

 other at their base. 



The dorsal surface of the first antennal somite in Ibaccus 

 and all the Scyllaridas is projected in front, and locked by a 

 pair of dovetailed processes into the anterior margin of the 

 carapace ; and the first pair of antennae is articulated at the 

 anterior margin of this somite. 



In the Palinuridae the first antennal somite does not appear 

 in connexion with the anterior margin of the carapace, but is 

 developed as a large and conspicuous structure in advance of 

 the eyes, and at its anterior extremity the first pair of an- 

 tennas is articulated. 



The second pair of antennse resemble each other in the two 

 separate families in their connexion with the body of the 



