256 LEON J. COLE. 



logical symmetry which obtains in other respects. As is to be 

 expected the teeth on the extra claws are plainly, like those of 

 the normal claw, of the "crusher" type. 



No attempt was made to study the internal anatomy further 

 than to note that the extra double dactyl has two adductor ten- 

 dons, but only a single abductor tendon. This condition is what 

 might be expected from the way in which the two extra dactyls 

 {D'R and D' L) are "compounded" {vide infra) at their base. 



Carpopodite. — The effect of the doubled condition distally is 

 very evident in the carpopodite. It is much broader distally 

 than a normal carpopodite, especially as viewed from above. 

 This is due in large part to an extra process {d.p' .) on the posterior 

 face of the appendage in the middle of the area which is evenly 

 concave in the normal lobster. This process is in line with the 

 double dactyl {D' L and D'R), thus having the same relations to 

 this doubled extra part that the dorsal articular process {d.p.) 

 has to a normal dactyl. Opposite d.p' ., in the concavity of the 

 anterior side, is a smaller process {v.p' .). The normal ventral 

 articular process {v.p.) is present, but, apparently due to the 

 disturbing influence of the abnormal parts, the articulation of 

 the chela with it is not close.^ The only close articulation is, 

 then, with the dorsal process {d.p.), and although the chela can 

 be moved on this in the normal plane of movement, it is capable 

 of a slight movement in other directions as well. The hinge- 

 like movement in the normal plane {i. e., on the axis between 

 d.p. and v.p.) is, moreover, greatly limited by the secondary 

 processes {d.p'. and v.p'.). Whereas in the normal lobster the 

 claw (propodite) can swing on the carpopodite through an arc 

 of about 90°, it is limited here to a movement of 25°. A smooth 

 spot on the shell {x, Fig. 3) shows where d.p'. has stopped the 

 movement of the claw in that direction, and the nature of the 

 surfaces at v.p. shows that in the living animal there must have 

 been some movement of the claw in the plane at right angles to 

 the normal plane of movement. 



^ It would look as though the presence of muscles belonging to the abnormal 

 part, which by their action tended to swing the claw on the secondary axis d.p'. -v.p'., 

 had prevented a close articulation at v.p. A careful study of the musculature of 

 the carpopodite would be of much interest, but it was found impracticable to make 

 such a study at the present time. 



