THE G-ENDEES Of GENERA 75 



The species Psevdocorystes armatus, Milne-Edwards, 

 was found at Valparaiso, and Milne-Edwards supposes that 

 it may be the same as the ' Grass Crab,' figured by Browne 

 in his ' History of Jamaica,' pi, 48, fig. 2. 



Atelecydus, Leach, 1813, is a member of the family in 

 which the third maxillipeds, contrary to the family custom, 

 do make a complete closure of the mouth-cavity. The 

 type species, Atelecyclvs septemdentatus (Montagu), was 

 first observed on the south coast of Devon. Its carapace 

 is nearly circular. Leach says that to the fishermen it is 

 well known by the name of old man's face orah. The 

 antero-lateral margin on each side is furnished with nine 

 teeth, and probably for this reason Leach thought himself 

 justified in changing the name to heterodon, in which he 

 has been followed by Bell. Montagu perhaps did not 

 think that the point at each extremity of the series ought 

 to be counted in, and at any rate no one can be injured by 

 the retention of the name which it was his privilege as 

 the discoverer of the species to choose. 



Thia, Leach, 1815, is represented both in the Mediter- 

 ranean and in British waters, probably by one and the 

 same species, called Thia polita by Leach in 1815, in allu- 

 sion to the polished surface of the carapace, but as there is 

 no substantial reason for thinking it distinct from the 

 species described and figured by Herbst as Cancer residuus 

 in 1799, its name ought to be Thia residuus (Herbst), 

 although some may prefer to call it Thia residua, not re- 

 flecting that the animals are both male and female, and 

 ignoring the old rule of Latin grammar that the mascu- 

 line gender is to be preferred to the feminine. In this 

 species, which like Corystes is a sand-burrower, the pleon 

 is very narrow in both sexes, and, though in the male it is 

 only five-jointed, the transverse grooves of the composite 

 joint are so strongly marked, that all the seven joints 

 might at first glance be thought to be distinct, as they are 

 in the female. 



To conclude the discussion of the names used in this 

 family, it may be mentioned, first, that although de Haan 

 rightly claims priority for BicSra which he established 



