52 CRUSTACEA. 



separate them from the Brachyura. We do not attempt to point to 

 any genus among the Macroura representing the Hippidea. Another 

 line from the Cancroidea passes through Acanthocyclus to Corystoides, 

 the latter genus having, like the Maeroura, no fossettes for the inner 

 antennae, and both differing from the true Corystoidea in the outer 

 antennae being obsolete. Bellia, according to Edwards, has like cha- 

 racters nearly with Corystoides. 



The Grapsoid species are represented of a degraded form in Porcel- 

 lana, and the particular connecting genera appear to be Grapsus and 

 Plagusia. The articulation of the fourth joint of the outer maxillipeds 

 with the outer angle of the third joint, shows that the type is Grap- 

 soid. But here the abdomen is enlarged and partly free; the lateral 

 appendages of the caudal extremity are large; the outer antennae are 

 posterior and exterior to the eyes; the posterior thoracic legs are 

 small and dorsal ; and various other characters separate the species 

 from the Brachyura. While, at the same time, the inflexed abdomen, 

 with only a single pair of appendages in the male, the inner antennae 

 with fossettes, the outer maxillipeds covering tolerably well the buc- 

 cal area, and the general habit, are far from Macroural in character. 



A still lower grade of this type is seen in Galathaea. The general 

 characters are similar to those of Porcellana; but both thorax and 

 abdomen are more elongated, and the habit is rather Macroural than 

 Brachyural, and there are even present in males, the full number of 

 abdominal appendages. But, as De Haan with his usual acumen has 

 detected, the carapax has the lateral suture of the Brachyura. It 

 appears then to be a group closely on the confines of the Macroura, 

 if not properly one of that division. 



Through Galathea, we believe we may point out a passage into 

 the Macroural dominion by JEglea, to Astacus. ^Eglea has the 

 branchiae of the Astacus group, consisting of clusters of minute cylin- 

 ders, and thus is not of the Galathaea family, although similar in habit 

 and in the posterior thoracic legs. We should thus connect the 

 Macroura with the Brachyura through two lines, one by Callianassa 

 and Pagurus, and the other by Astacus and Galathaea. 



The Leucosoid type is found only in a single degraded form, that 

 of the Ranina family. The species are nearly like Brachyura in 

 many characters. Yet the inner antennae have no fossettes; and the 

 vulvas are in the base of the third pair of legs. The mouth is nearly 

 as in Leucosia or Matuta, and the feet are swimming feet, as in 

 Matuta. The first step towards this degradation is seen in Dorippus, 



