23G Dr. W. Stimpson on the Classification of the Brachyura. 



particularly well in Homarus, where the parts are more distinct 

 from their large size. The " peduncle " of the antenna in the 

 Lobster is considered by Milne-Edwards to consist of five joints; 

 but a sixth is indicated at the base of the penult, on the lower 

 side of the member. Here there is a small triangular piece, 

 articulating with the second and third joints as well as the 

 penult, perfectly mobile, and dependent upon no one of these 

 joints more than another. An additional evidence that this 

 piece is the representative of a distinct joint is furnished by the 

 fact that the articulations of the two proximate joints are in the 

 same plane, and not, as should be the case were they normally 

 contiguous, in planes perpendicular to each other. To complete 

 the number (seven) of joints, we have the flagellum, which cor- 

 responds to the dactylos or terminal joint of the thoracic mem- 

 bers. This homology is rendered probable by the occurrence, 

 in the remarkable Hippidcan genus Mastigopus^, discovered by 

 me in the Chinese seas, of a multiarticulate dactylus to the 

 chelipeds perfectly similar to the flagelliform terminal appendage 

 of an antenna. 



The squamiform appendix of the antenna is attached to the 

 second joint, and is homologous to the exopod of the feet, or the 

 exognath of the maxillipeds, which has the same position. It is 

 called scaphocerite by Milne-Edwards, but would be more ap- 

 propriately named exocerite, a term indicating its relations with 

 greater exactness, and corresponding in construction with that 

 of its homologues. This appendage is normally two-jointed, as 

 is seen in the embryo Humarus and in the adult Squilla ; its 

 basal joint is obsolete or coalesced with the terminal squamiform 

 joint in adult Macrura and Anomura, while in Brachyura the 

 entire appendage disappears with perfect development. The little 

 basal joint of the exocerite in the embryo Homarus is mistaken 

 for the "armiger" (basicerite) by Dr. Strahl, who considers the 

 large joint which supports both branches of the antenna as the 

 " intercalare " (coxocerite), on the ground that in the adult the 

 third joint is articulated with both the coxocerite and the basi- 

 cerite. But this is so only in appearance : if the antenna in a 

 fresh Lobster or Cray-fish be bent outward, it will be seen that 

 the posterior condyle of the third joint articulates with the basi- 

 cerite alone. The basicerite, in the embryo Decapod, is far from 

 being the trifling joint seen at the base of the scale-like append- 

 age, but is, in fact, that large supporting joint which is the first 

 to make its appearance, and which often reaches, with its exo- 

 cerite, a large size before any trace of other joints, either coxal 

 or terminal, can be perceived. In the figures accompanying the 



* Proc. Acad. Nat. Sc. Philad. December 1858. Not the Mastigopus of 

 Leuckart, which is a Sercjestes, 



