8 



edges — as to whether they are smooth or are spiny — are also fairly to be 

 depended upon. 



Good specific characters (with the qualifications noted against each) are 

 furnished by the following parts : — 



(1) The antennular fiagella: but in the male they are sometimes longer 

 than they are in the female, and occasionally {e.g., in the adult male of Metape- 

 neus coniger and Parapeneus rectacutua) are specially modified : 



(2) The external (3rd) maxillipeds, as regards their length and the form 

 and manner of articulation of their dactylus : but the length is often different 

 in the two sexes and young of theisame species, and occasionally {e.g., several 

 species of Peneus proper) the dactylus of the male is quite unlike that of the 

 female, both in form and in mode of articulation : 



(3) The chelipeds, as regards their length, and specially as regards the 

 spines of their basal joints : in some species, however, {e.g., Mefapeneus Dobsoni 

 and M. Joyneri) the spine of the basis of the 3rd pair of chelipeds is peculiarly 

 modified in the male : 



(4) The fourth pair of legs, as regards their length and the form of their 

 merus : but the merus occasionally exhibits sexual differences : 



(5) The fifth pair of legs, as regards their length, the sculpture of their 

 merus, and the presence or absence of an exopodite : but the length sometimes 

 changes with age and differs with sex, and the form of the merus (e.g., in 

 several species of Metapeneus) is sometimes quite peculiar in the male : again, 

 in the female of Metapeneus Dobsoni, this pair of legs is usually represented only 

 by a coxa and stump : 



(6) The form of the andricum, or petasma, and thelycum : but only when 

 dealing with adults. 



