66 



SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I3I 



to be found in various modern arthropods other than the Crustacea. 

 His discussion, however, takes too many liberties with simple visible 

 facts in an endeavor to fit them into a consistent scheme of structure. 

 The studies of trilobite appendages by Stormer (1939) leave little 

 doubt that the trilobite leg (fig. 25 A) is simply a uniramous, seg- 

 mented limb with a coxal epipodite that was perhaps a gill. Stormer's 

 contention, however, that a narrow ring at the base of the coxa is a 



Pat 



Fig. 25. — Examples of segmentation of arthropod legs. 



A, leg of a trilobite (from Stormer, 1939). B, leg of Marella (adapted from 

 Walcott, 1931). C, leg of Burgessia (from Walcott, 1931). D, leg of solpugid 

 arachnid. E, leg of a chilopod, Liihobius. F, leg of a decapod, Cambanis. 



Crppd, carpopodite (tibia) ; Cxpd, coxopodite (coxa) ; Dactpd, dactylopodite 

 (pretarsus) ; Eppd, epipodite; Mrpd, meropodite (femur) ; Pat, patella; Propd, 

 propodite (tarsus). 



precoxal segment is questionable. The coxa of other arthropods is 

 often marked by a circular groove near the base that forms an internal 

 strengthening ridge giving attachment to the body muscles of the 

 limb. In the trilobite leg the large coxopodite should be the movable 

 basal segment of the limb and not the narrow "precoxa," 



The idea that the primitive arthropod limb was a flat, lobulated 

 appendage of the phyllopodial type has been accepted by some carcin- 

 ologists regardless of the fact that the limbs of the trilobites (fig. 

 25 A) and of associated fossil forms such as Marella (B) and 

 Burgessia (C) are slender jointed legs, as are those of nearly all 

 modern arthropods (D, E, F), including the Malacostraca (F). 



