MUSEUM OF COMPARATIVE ZOOLOGY. 261 
plane nearly at right angles with the plane of motion of the normal dac- 
tylus (a). Here, then, in addition to the duplication of the dactylus 
seen in Fig. 12 (a! indicating homologous parts in the two figures), one 
sees an imperfect attempt to duplicate the propodite in the process x. 
Plate I. Fig. VT (left chela). — This monstrous claw is similar to the 
one described and figured by Lucas (Homarus vulgaris, in No. 7 of the 
Bibliography). The dactylus (a) does not close upon the index. From 
the base of the index there arises from the upper side a very large un- 
jointed appendage, which shows a strong tendency to divide into two 
branches (b, c), each furnished with a row of teeth. The teeth of the 
branch 6 point toward the teeth of the index, while those of the branch 
c are directed toward the row of teeth on the dactylus when the latter 
is opened. The tendency seems to be to duplicate the dactylus in 5, the 
index in c. As there is no articulation at the base of the monstrous ap- 
pendage, the teeth on the branch 6 are useless, and as the branch c is 
not in the plane of motion of the dactylus its teeth are likewise func- 
tionless. "Thus, although these two extra lines of tecth are developed, 
there are no two in the claw which can be applied to one another. 
Plate IT. Fig. 1 (Homarus Americanus, dactylus of right chela).* — 
Beyond the middle, this dactylus is bent downward at nearly a right 
angle. From the upper side are developed two processes (b, 0^), which 
are forked at their ends and. furnished with two rows of teeth within. 
The propodite is lost. Resembles the dactylus of the claw figured on 
Plate I. fig. 15, but differs in the fission of the processes b and b. 
Plate IH. Fig. 2 (Homarus Americanus, one of the small chelipeds). — 
This leg is provided with two chelæ. One of them has the ordinary 
form and structure, but is bent at a strong angle with the long axis of 
theleg. The second claw appears to have budded off from an ampu- 
tated surface of the propodite. It consists of two fingers, which have 
the form of the normal dactylus and index, but neither is articulated 
with the other at the base. The two fingers together seem to be mor- 
phologically equivalent to a single segment, and represent a two- 
branched supernumerary dactylus. 
Plate II. Fig. 3 (Homarus Americanus, left chela). — In this small 
chela the index is curved sharply upward and deeply channelled on its 
lower face. Unlike all those previously noticed in this paper, this is à 
simple malformation through distortion, without any development of 
accessory parts. 
Plate 11. Fig. 4 (Homarus Americanus, dactylus of right chela). — 
* All the figures on Plate II. are of natural size. 
