TEOPHIES FROM EGYPT 173 



dorsal shield has two long horns behind and one of porten- 

 tous length in front. Even after the general appearance 

 of the adult has been assumed, the young crustacean 

 shows several interesting differences from its elders. The 

 accompanying figure of a little one, an eighth of an inch 

 long, taken off the back of its mother, exhibits a carapace 

 with numerous little spines not found in the parent, and 

 the telson simply ovate, instead of being subdivided by 

 sutures into seven portions. Porcellana liobertsoni, Hen- 

 derson, is remarkable as having been taken not in shallow 

 water, but at a depth of 390 fathoms in the West Indies. 

 Dr. de Man states that ' the genus Porcellana is represented 

 in the Bay of Bengal by no fewer than fifteen species.' 

 Several of them, however, as he explains, belong to the 

 other genera of this family, which Dr. de Man retains as 

 subgenera. 



Petrolisthes, Stimpson, 1858, has the 'front' undulated, 

 the first joint of the second antennae remarkably short, 

 not reaching the margin of the carapace, the fifth joint of 

 the chelipeds often dentate on the inner margin, and the 

 walking-legs as in Porcellana, Among the Crustacea 

 collected on Napoleon's celebrated Egyptian expedition, a 

 species, beautifully and elaborately figured by Savigny, was 

 named Porcellana Boscii by Audouin, to whom the French 

 Government entrusted the task of describing the species in 

 Savigny 's splendid work, in consequence of the latter 

 author's Jong-continued illness. This species was trans- 

 ferred by Stimpson to his genus Petrolisthes, and it well 

 exhibits the unusual prominence which in this family is 

 often assumed by the third maxillipeds, projecting as if 

 they were a powerful pair of feathered antennae. The name 

 of the genus meaning 'rock-slider' points to one of the 

 characteristic habits of the family. 



Porcellanella (White), Stimpson, 1858, differs from 

 Porcellana chiefly in having the last joint in the walking- 

 legs not simple but multiunguiculate. Between these two, 

 and agreeing with Porcellanella and Polyonyx, Stimpson, 

 in the multiunguiculate joint, the Russian writer Czerni- 

 avsky has insinuated his genus Porcellanicles, 1884, in his 

 U 



