10 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 8o 



basal segment represent the coxa, the name by which it has gone in the 

 past, or is it in reahty the subcoxa? If it is a true subcoxa, the 

 second segment becomes the coxa, instead of the first trochanter, as 

 it is commonly regarded. Evidence as to the homology of these two 

 basal segments is wanting, hence no serious objections should be 

 raised to the prevailing practice of calling them the coxa and first 

 trochanter. 



The legs of scorpions appear to be seven-segmented, not counting 

 the claws, but in reality are only six-segmented. The bend of the leg 

 takes place between the third and fourth segments, while in pseudo- 

 scorpions it is between the fourth and fifth. The scorpion leg seg- 

 ments have not heretofore been homologized. 



The leg of a thelyphonid shows a large number of rings, but three 

 of these represent subdivisions of the tarsus. Borner has worked out 

 the muscles. Judging from the muscle attachments figured by Borner 

 the present writer would regard the leg of a thelyphonid of the 

 genus Thclyphonus as composed of the following segments : Subcoxa, 

 coxa, trochanter, femur, patella, tibia and tarsus, in addition to the 

 foot. The tarsus itself has false segments, and the first trochanter 

 is vestigial. The thelyphonid leg is, therefore, more like the leg of a 

 solpugid or a phalangid than like one of a scorpion or pseudoscorpion. 



THE PYCNOGONIDA AND RICINULEI 



Mention should be made of two arachnid orders in which the legs 

 show a large number of segments. In the Pycnogonida the legs afe 

 very long and are composed of eight segments in addition to the 

 claws. Borner (1921) has worked out the musculature. The writer 

 has also done the same for Colossendies nmcerrmia and finds prac- 

 tically a complete agreement in regard to the facts presented by 

 Borner, but a different interpretation is made of them. The wall of 

 the body extends outward in the form of a cylindrical process for 

 the articulation of the first leg segment. This first segment is very 

 .short and similar to the next two short ones, which possess dicondylic 

 hinges. The fourth and fifth segments are very long and have dicon- 

 dylic hinges. The very long sixth segment has but a single hinge and 

 only a flexor muscle. The short seventh segment is immovably hinged 

 to the short eighth and has no muscles originating in it. The eighth 

 bears alone the extensors and flexors of the claws. Each of the first 

 five segments is provided with a levator and a depressor muscle. In 

 no instance does any muscle in the pycnogonid leg pass entirely 



