Observations upon Mr. Hailstone's Crustacea. 267 



also several of those of the long-legged crab described by 

 him [Jig. 27.]- The small size of both species of Porcellana 

 might induce the belief that they were in a young and imma- 

 ture state; but the fact recorded by Mr. Hailstone, that the 

 preserved specimen was found with spawn, disproves the 

 presumption. But, is Mr. Hailstone quite sure that this was 

 the case ? as the preserved specimen itself, upon examination, 

 exhibited no appearance of eggs. If so, the small size of the 

 animal thus shown to be adult is far below that of any of the 

 other species. It comes nearest to the Porcellana LeachzV of 

 Mr. J. E. Gray's monograph upon this genus, published in 

 his Zoological Miscellany, p. 15.; but its colours, size, &c, 

 are different, whence the name of P. minuta may be applied 

 to it. 



The two other species of Crustacea (Jigs. 26. and 27.) 

 appear to me to be animals in a very young state, both from 

 their minute size, and comparatively imperfect appearance 

 and organisation. They are certainly very distinct from the 

 full-grown animals of the genera Hyas and Macropodia; but 

 I feel little hesitation in referring the former to Hyas coarc- 

 tata, and the latter to Macropodia Phalangium of Pennant 

 (longirostris Leach). At a period when the developement 

 and supposed transformations of the decapod Crustacea are 

 matters of dispute among the first crustaceologists, it is espe- 

 cially interesting to exhibit the distinctions of form in which 

 these animals appear in a very young state of their existence : 

 in this point of view, I regard the animals sent by Mr. Hail- 

 stone as extremely valuable. 



M. Milne Edwards, in an elaborate memoir upon this 

 subject, has laid down the following theory ; namely, that, in 

 this group of animals, there is a constant tendency, during 

 growth, to remove (eloigner) the form of the animal from a 

 common type : in short, to individualise it. Now, the com- 

 mon type of form of the crabs is square, transverse, or more 

 or less rounded; and both the animals now described fully 

 support this doctrine. Hyas, in its adult state, is triangular ; 

 the animal which I have supposed to be the young of Hyas 

 coarctata is almost square : but, by the application of this 

 theory, the ordinary square form of the Brachyura will be 

 lost by the greater swelling out of the hinder part of the 

 body, until the triangular form of the adult Hyas is obtained. 

 In like manner, the adult Macropodia; are distinguished by 

 their rostrated front ; a character certainly not typical among 

 the crabs, although it is among the Macrura, or shrimps, 

 &c. We may, therefore, expect, if M. Edwards be correct," 

 that the young of Macropodia will have the head not ros- 



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