PART 1 GARTH : PACIFIC OXYRHYNCHA 1 1 



Occasionally the dissimilarity of the sexes had the opposite result in 

 that male and female of two different species were combined as one. 

 A case in point is Eucinetops lucasi Stimpson, which was subsequently 

 divided by Rathbun (1923a), the females remaining E. lucasi and the 

 males becoming E. rubellula, a division further recognized herein by the 

 establishment of neotypes for the resultant species. 



Characters subject to sexual dimorphism in the Majidae include the 

 degree of enlargement of the cheliped, the height of the palm, the size 

 of the gape between the fingers, and the presence or absence of an inter- 

 digital tooth or teeth ; the relative length of the walking legs, particularly 

 those of the anterior pairs ; the shape and number of free somites of the 

 abdomen ; and the number and modification of structure of the pleopods. 

 Since these are among the most useful characters taxonomically, the sex 

 of the holotype becomes an important consideration in cases of disputed 

 identity of a species. Unfortunately, Rathbun (1925) does not include 

 this information in her section on type locality and type, but includes it 

 rather in her tables of material examined. It has therefore been necessary 

 to ascertain the sex of the type specimen in the case of types not seen 

 by her in the preparation of her monograph. This has been done by 

 consulting the literature, or, in the few instances in which the original 

 description failed to specify sex, by requesting reexamination of types 

 by curators of institutions retaining their custody. 



Although the number of free abdominal somites in the two sexes is 

 one of the most clear-cut of generic distinctions, this important informa- 

 tion was included by Rathbun (op. cit.) for both sexes in but 40 per cent 

 of the majid genera treated. In another 16 per cent it is given for one 

 sex or the other, while in 44 per cent of the genera it is omitted entirely. 

 It has been possible in all but a very few American genera to ascertain 

 the number of free abdominal somites in both sexes and to include this 

 information in the generic descriptions given, thus permitting the con- 

 venient grouping of genera within their subfamilies for key and diagnostic 

 purposes. The adoption of any system of classification based upon sexual 

 characters has certain disadvantages where the material to be identified 

 is of the sex opposite to that described. The experienced worker will 

 therefore take into account supplementary generic and specific charac- 

 ters, and will consult the older, more highly artificial keys when neces- 

 sary. 



