258 LEON J. COLE. 



lation in a plane at right angles, or nearly so, to the normal 

 articulation. This condition corresponds to that between the 

 carpopodite and the propodite, described above. There is no 

 evidence of the corresponding process on the opposite side, how- 

 ever, nor is there any articulation with p' , the distal portion swing- 

 ing normally on the axis between a.p. and p.p. But while this 

 movement covers an arc of approximately 45° in a normal claw, 

 it is here limited to a range of between 25° and 30°. There is 

 no sign of duplication of the large spine {sp.) on the dorsal side 

 of the meropodite. 



Ischiopodite. — The ischiopodite, instead of being broad and flat, 

 as in normal cases, is broadly triangular in cross section, while 

 the line of articulation between it and the meropodite is much 

 less oblique than normal. The motion at this place is normally 

 (in the legs following the cheliped) on an essentially dorso-ventral 

 axis (d.a.-v.a.), though due to torsion in the chelipeds it becomes 

 greatly inclined. In the abnormal specimen the dorsal articu- 

 lation (d.a.) appears practically normal, but on the ventral side 

 there are two points of articulation (v.a. and a'.). Being thus 

 hinged at three places the joint is stifT and incapable of move- 

 ment in any plane. The row of spines running down the ven- 

 tral side of the meropodite and continued on the ischiopodite, 

 proves the articulation (v.a.) in line with these to represent the 

 normal one, while the other (a') is secondary. 



The articulation between the ischiopodite and the basal podo- 

 meres is apparently normal, though the ischiopodite here has 

 on its posterior side a ridge (r) which is not present in normal 

 specimens. This ridge ends in a short, blunt process, much like 

 an articular process, but there is no articulation with it. It 

 does in all probability, however, represent such a secondary 

 process, being placed, as in the other joints, midway between 

 the normal points of articulation. 



Relations of Symmetry. 

 Torsion. — It is a matter of common knowledge that in de- 

 velopment the cheliped of the lobster undergoes a twisting or 

 torsion, as a result of which the chelae come to lie in a nearly 

 horizontal plane, that is, almost at right angles to their normal 



