DESCRIPTION OF AN ABNORMAL LOBSTER CHELIPED. 2$T, 



logically posterior) face. This outgrowth does not arise from 

 the middle of the outside face of the primary propodus, but 

 rather from the ventral half of its surface, the significance of 

 which in its relation to the planes assumed by the various claws 

 will be discussed further on. In general appearance the out- 

 growth represents a more or less completely doubled extra claw/ 

 and according to the classification given by Emmel (1907) would 

 fall in the class having "abnormal processes arising from the 

 normal propodite," and under this heading it would probably 

 have to be classed with those having "two extra indices and 

 double extra dactyl." It differs, however, from any previously 

 described specimens in this category, so far as I am aware, in 

 the degree to which the double dactyl approaches the condition 

 of two separate dactyls, it being markedly bifurcated at the tip, 

 whereas in the case (specimen No. 4) described by Emmel, 

 what he takes to be the double dactyl is only a small undivided 

 "stump." The strength of his interpretation lies in the fact 

 that both the double dactyl and the index in other specimens may 

 be represented by an undivided process, the double character 

 of which is indicated by its having teeth on two opposite sides 

 (cf. Emmel's specimens No. 2 and No. 3). 



Considering now only the supernumerary outgrowth, the basal 

 part, which represents a double propodus, has along its ventral 

 side a deep groove, as may be seen in Fig, 2. The continuation 

 of the divergent ridges which bound this groove form two separate 

 and distinct indices (I'R and Z'L), each of which, taken by itself, 

 appears like a practically normal index. They are, moreover, 

 essentially alike except that their relations of symmetry are re- 

 versed, so that one would appear as the image of the other in a 

 plane mirror placed between them. This relation will, however, 

 be discussed more fully later. The opposing dactyl is also di- 

 vided for nearly half its length, on account of the bifurcation 

 mentioned above, the divergent branches (D'R and D' L) meeting 

 in opposition the corresponding extra indices (I'R and I'L) . The 

 double character of the dactyl clear to its base is indicated by the 

 fact that the rows of teeth on the two tips continue in separate 

 and distinct lines down the inside of the basal portion. Further- 



^ The extra claws are somewhat smaller than the norma! or primary claw. 



