TRACHYCARCINUS. 25 



Family CORYSTID.E. 

 TRACHYCARCINUS Fax. 



Bull. Mus. Coiup. Zool., XXIV. 156, 1S93. 



Carapace pentagonal, moderately convex, lateral margins long, nearly 

 straight, toothed. Front narrow, produced, three-toothed. Orbits large, 

 with forward aspect, imperfect, with two hiatuses above, one below, and one 

 at the inner angle ; lower wall formed chiefly by the carapace. Anterior 

 margin of buccal cavity not distinctly defined, epistonie short, ridges of the 

 endostome developed. Sternum long and rather narrow. Abdomen of male 

 narrow and five-jointed, the third, fourth, and fifth segments consolidated. 

 Eye-stalks very small, retractile within the orbits. Antennules longitudinally 

 folded. The antennae lie in the inner hiatus of the orbit ; their basal segment 

 is but slightly enlarged, not filling the hiatus at the inner angle of the orbit 

 nor attaining to the front, subcylindrical, unarmed, imperfectly fused with 

 the carapace ; the second segment is longer and slenderer than the first, the 

 third segment about equal to the second in length, but slenderer ; all these 

 segments are furnished with long and coarse setae ; the whole antenna is 

 less than one half as long as the carapace. The ischium of the outer niaxil- 

 lipeds is produced at its antero-intornal angle ; the merus of the same 

 appendages is rounded at the antero-external angle, obliquely truncated 

 but not emarginated at the antero-internal angle, where it articulates with 

 the following segment. Legs of moderate length. Eight and left chelipeds 

 very unequally developed in the male. Dactyli of ambulatory legs stylifoi-m, 

 straight, slender, longer than the penultimate segments. 



The pentagonal shape of the carapace recalls the genus Telmcssns White. 

 But in Telmessus the front is divided by a median notch, the orbit is much 

 more complete, the basal segment of the antenna sending off an external 

 process that completely fills the hiatus at the inner angle of the orbit. 

 Although Trachycarciiuis bears but little resemblance superficially to Tri'cho- 

 pellcuion A. M. Edw.* on account of the very different shape of the carapace, 

 it is in reality closely related to the latter genus as is shown by the close 

 resemblance between them as regards the orbits and antennae, the merus 

 of the outer maxillipeds, the form of the chelipeds, etc. 



The Corystoid crabs form a heterogeneous assemblage of rather prirai- 



* Bull. Mus. Couip. Zool., VIII. 19, Plate II., 1880. 



