THE GEAPSOID CRABS OF AMEKICA. 9 



In the lists under " Material examined " a number in parenthesis 

 following an indication of a specimen or specimens denotes a cata- 

 logue number otf the United States National Museum unless otherwise 

 indicated. M. C. Z. Museum of Comparative Zoology; P. M. 

 Y. U. = Peabody Museum of Yale University; Mus. S. U. I. = 

 Museum of the State University of Iowa ; y. = young. The words 

 " U. S. Fisheries " should be understood before " Str. Albatross" 

 " Str. Fish Ilawk," or " Sch. Grampus." 



In the same lists there have been entered, besides specimens in the 

 National Museum, many types examined elsewhere, as well as such 

 specimens from other collections as increase our knowledge of the 

 range of the species, but for lack of space no attempt has been made 

 to record all of the many specimens examined in museum and 

 private collections. 



THE GRAPSOID OR CATOMETOPOUS CRABS OF AMERICA. 



The term Catometopa or " square-fronted " was early x applied to 

 a group of crabs which was contrasted with the Cyclometopa or 

 " round- fronted " crabs. These terms were abandoned 2 because the 

 one group was found to merge gradually into the other. The name 

 Brachyrhyncha was given to the whole. Aside from intergrading 

 forms, the so-called Catometopa contain many types that are not 

 "square-fronted." In 1851 s Dana first used the word Grapsoidea 4 

 for this group, Grapsus being the typical genus. The name Grapsoid 

 is therefore used in the title of the present paper as a short and con- 

 venient term to indicate the content of the volume. 



The key on pages 13-15 gives the relation of the families here 

 dealt with to the remainder of the Brachyura. or short-tailed crabs. 



1. The family Goneplacidae links the Catometopes to the Cyclome- 

 topes and is most closely allied to the family Xanthidae, some of its 

 genera having the form of the Panopeids or mud crabs, and differing 

 from them chiefly in the characters of abdomen and sternum and the 

 shape of the chelae. The Goneplacids, being bottom-dwelling forms, 

 are taken almost exclusively in the dredge or tangle. 



2. The Pinnotheridae is a large family of small crabs, chiefly com- 

 mensal, sometimes free-swimming and occasionally parasitic. While 

 in most crabs the male is stronger than the female, especially as 

 regards the chelipeds, and often attains a greater maximum size, the 

 reverse is true in many Pinnotherids. The female may not only be 

 much larger than the male, but have a very different shape and ap- 

 pearance, due, no doubt, to the difference in mode of life of the two 

 sexes. The female may be commensal or parasitic, while the male 

 is free-swimming. Much is yet to be learned regarding the habitat of 



1 Catometopes Milne Edwards (part), Hist. Nat. Oust., vol. 2, 1837, p. I. 



* See Borradaile, Ann. Mas. Nat. Hist., ser. 7, vol. 19, 1907, p. 466. 



*Amer. Journ. Scl., ser. 2, vol. 12, 1851, pp. 283 and 285. 



4 The Giapsoldiens of Milne Edwards is equivalent only to the Family Grapsidae. 



