122 BULLETIN 166, UNITED STATES NATIONAL MUSEUM 



Carapace circular, oval or polygonal. Eyes and orbits very small; 

 front narrow but many times wider than orbit. Antennules folding 

 more or less obliquely. Antennae small, sometimes obsolete. External 

 maxillipeds completely closing the buccal cavern, except that often 

 there is a crevice in front; the palp springs from a groove in their 

 dorsad surface near the inner edge, and is completely concealed when 

 the maxillipeds are in repose; exognath broad. The afl'erent branchial 

 channels occupy the sides of the endostome on either side of the deep 

 median endostomial groove which serves as an efferent branchial 

 channel. The afferent channels are covered in by the exognaths of 

 the external maxillipeds; the efferent channels, by a pair of lamellar 

 processes from the first maxillipeds. Chelipeds symmetrical. Com- 

 monly the third to sixth abdominal terga are fused, sometimes the 

 sixth is independent. The vasa deferentia emerge through the fifth 

 thoracic sternum on either side, near the bases of the posterior legs. 

 (After Alcock.) 



KEY TO THE SUBFAMILIES AND GENERA OF THE FAMILY LEDCOSITD AIS 



A'. Merus of external maxillipeds half or more than half the length 



of the ischium measured along the inner border. Fingers 



stout, gradually narrowing from base to tip. 



R' . The pter.ygostomian margin terminates anteriorly in a circular 



depression behind the orbit. Surface of carapace uneven. 



Chelipeds of moderate length EBALIINAE (p. 123) 



C'. Carapace broadly elliptical, sides expanded Uhlias (p. 149) 



C2. Carapace narrower, pentagonal to octagonal, surface very 

 uneven. 

 D'. Deep hollows or caves within the posterior half of the 



carapace Speloeophorus (p. 141) 



D'. No deep hollows or caves within the posterior half of tlie 

 carapace. 



E'. Upper surface of carapace deepl}' excavate Lithadia (p. 130) 



E2. Upper surface of carapace uneven but not deeply 



excavate Ebalia (p. 123) 



B'. 'I'lie pterygostomian margin does not terminate in a circular 

 depression and is often obscure. Carapace almost hemi- 

 spherical, surface only slightly uneven. Chelipeds often 



elongate \ PHILYRINAE (p. 151) 



C. Anterior margin of efferent l)rancliial channel fornu"ng tlie 

 lower margin of orbit. 

 D'. Chelipeds rather massive. Al)dominal segments 3-5 



fused in male Persephona (p. 151) 



D^. Clielipeds long and slender. Abdominal segments 3-6 

 fused in male. Cardiac and intestinal regions indi- 

 cated Myropsis (p. 164) 



C2. Anterior margin of efferent branchial channel separated by 

 a deep, narrow channel from the lower margin of orbit. 

 D'. Lateral and posterior margin of carapace marked by a 

 continuous beaded line. Exognath very broad, ante- 

 rior portion strongly arcuate Philyra (p. 167) 



