NEW GENERA AND SPECIES OF AMERICAN 

 BRACHYRHYNCHOUS CRABS. 



By Mary J. Rathbun, 



Assistant Curator of Marine Invertebrates, United States National Museum. 



The forms here described belong to the group formerly known as 

 the Catometopa or Grapsoidea. The type-specimens of three of the 

 species are in the Museum of Comparative Zoology and were kindly 

 lent for description through Dr. Walter Faxon; paratypes of the 

 same as well as t3^pes of the remaining species are in the United States 

 National Museum. 



FAMILY" GONEPLACIDJD. 



Subfamily C^RCITsTOPLj^CIISr^E:. 



TRIZOCARCINUS,' new genus. 

 Ty])e of the genus. — Trizocarcinus deritaius (Rathbun). 

 Carapace deep, subquadrilateral, broader than long, w4th little dis- 

 tinction of regions, convex fore and aft and from side to side. Fronto- 

 orbital border about three-fourths of the greatest width of the carapace; 

 antero-lateral borders arched, 

 dentate. Front square-cut, 

 straight, between one-third and 

 one-fourth the width of the cara- 

 pace, faintly notched in the mid- 

 dle, deeply separated from the su- 

 pra-orbital angles. Upper margin 

 of orbit with two distinct notches. 

 Basal segment of antenna short, 

 the flagellum standing loosely in 

 the orbital hiatus. The anten- 

 nules fold transversely. Buccal 

 cavity increasing in width dis- 

 taUy, maxillipeds widely gaping, 

 their merus-joint with concave an- 

 terior margm, the antero-external 

 lobe projecting forward not outward. Efferent branchial channels well 

 defined. A stridulating ridge formed of parallel strife runs obliquely 

 backward from the antero-external angle of the buccal cavity; it is 

 played upon by a short ridge on the merus of the chehpeds. Cheli- 



1 TpiCto, to creak, to grate; Kapxivoc crab. 



Fig. 1.— Trizocarcinus dentatus, ventral vie-w 

 of left side of carapace of male type, show- 

 ing stridulating ridge, x 5. 



Proceedings U. S. National Museum. Vol. 47— No. 2047. 



117 



