16 CALIFORNIA ACADEMY OF SCIENCES. 



narrow front. The Grapsoidea may commonly be rec- 

 ognized by their quadrate form, but there are many 

 forms which do not exhibit this character. The Oxy- 

 stomata may be distinguished by the form of the buccal 

 area which is narrowed in front. None of these marks, 

 however, are absolutely diagnostic, for it is difficult to 

 separate the groups by single characters. 



Subtribe MAIOIDEA, or OXYRHYNCHA. 



Carapace narrowed in front and usually furnished with a rostrum 

 Branchial regions large; hepatic regions small. Buccal area quadrate. 

 Episloma usually large. The afferent channels open behind the pterygo- 

 stomian regions in front of the chelipeds; efferent channels opening at the 

 sides of the endostome, Antennules longitudinally plicated. Palp of the 

 maxillipeds situated at the summit or antero-internal angle of the merus. 

 Verges of the male on the coxse of the last pair of legs. 



This group includes the species known as the '^ spider 

 crabs " and "sharp-nosed crabs." They are generally 

 of sluggish habit and many of the species become over- 

 grown with sea-weeds and other foreign growths, which 

 make them difficult to detect in their natural habitat. 



The classification followed is that given in Miers' 

 revision of this group. ^ 



Legion MAIINEA. • 



Basal joint of the antennas well developed and inserted beneath the 

 eyes, usually occupying a great part of the infra-orbital space. 



Family INACHID^. 



Orbits not defined. Preorbital and postorbital spines generally well 

 developed. Eyes not retractile, or retractile against the sides of the cara- 

 pace. Basal antennal joint generally slender. Kostrum simple or bifid. 

 Fingers of the chelte never excavated at the tips. 



1 Jour. Linn. Soc, London, Vol. XIV, 1879. 



