120 A HISTOEY OF EECENT CEUSTACEA 



yellowisli-brown, but this is little or no guide to what its 

 colour may have been when living. The specific names in 

 this genus ought to have either masculine or else neuter 

 terminations, but many naturalists seem to suppose that 

 any generic name ending in -a is a feminine form, which 

 is far from being the fact. 



In this family the genus Libinia, Leach, 1815, contains 

 several species, and Mitlvrcux (Leach), Latreille, 1817, a 

 very large group. Of Libinia emarginata, Leach, Miss 

 Mary Rathbun, in her recent revision of the Periceridas, 

 says that in Long Island Sound occasionally this species by 

 its numbers ' so interferes with the steam oyster dredgers 

 that work is abandoned until the crabs (which are known 

 to the oystermen as " spiders ") have passed over.' 



Letjion 2 . PartJienopinea. 



The basal (or true second) joint of the second antenna? 

 is very small and embedded with the next joint in the 

 narrow gap between the ' front ' and the inner orbital 

 angle, the intraocular space being mainly occupied by the 

 inferior wall of the orbit. 



Family 4. Parthenopidce. 



The eyes are usually retractile within the small circular 

 and well-defined orbits ; the lower wall of the orbit is con- 

 tinued to within a very short distance of the ' front.' The 

 second antennae are very slender ; the basal joint does not 

 as in the Pericerida3 constitute a great part of the inferior 

 orbital margin, but is very small, seldom reaching the 

 ' front,' and with the next joint occupies the narrow gap 

 intervening between the ' front ' and the inner angle of the 

 orbit. (In Ceratocarcinus the antennas are completely 

 excluded from the orbits.) 



Some fifteen or twenty genera are reckoned in this 

 family, of which only one is known in the waters of Great 

 Britain. 



Ewnjnome, Leach, 1814, has not yet received many 



