Locomotonj Appendages of Trilohites. 83 



presented when first examined, I am of the opinion that this limb 

 was chelate. In removing the limestone so as to expose the left lobe 

 of the hypostoma, and also establish the articulation of the claws, an 

 accidental stroke destroyed the evidence of this direct connection, yet 

 at the fracture the ends of two bi'oken claws can yet be seen. At 

 first I was disinclined to regard the distal extremity of this pair as 

 chelate. Before attempting to remove the limestone, the surface 

 clearly showed a conjunction of these parts. This condition could 

 have been accounted for by supposing one limb to have been thrown 

 over another. It was to clear up this point that the removal of the 

 adherino; naeterial was made. If chelate, the claws were slender and 

 of about equal size as in Limulus. As the hypostoma is frequently 

 found in this limestone formation, it is to be hoped that these limbs 

 will also be found, so as to definitely settle this point. On fitting 

 the two specimens together, the ends of these supposed claws are 

 seen at the fracture directly beneath the left eye. These specimens 

 demonstrate that the thoracic appendages were well developed 

 walking legs, extending nearly to the outer margins of the carapace. 

 The exoskeleton of the limbs seems to have been somewhat different 

 in character from the calcareous exoskeleton of the dorsal surface of 

 the animal. At least, it was of such a character as not to preserve 

 well the integrity of the parts in the process of fossilization. They 

 conld not have been soft and yielding, judging from the symmetry 

 of the matrices of the meropodites, as well as from the general 

 cj'lindrical character of limbs themselves. 



On the ventral surface of the pygidium there are at least twelve 

 (pairs of) appendages ; posteriori}'', an exact enumeration is impos- 

 sible. The term pairs is used on account of the median groove, 

 showing in the structures a bilobed character. This grove is con- 

 tinuous with the thoi'acic groove, and is somewhat narrower and 

 more shallow than the latter. From an examination of the two 

 specimens, these twelve or more appendages appear to be leaf-like, 

 or foliaceous, and on each side of the median groove the direction 

 was outward and somewhat forward. No doubt these appendages 

 were branchial in function, and also adapted to swimming. 



These specimens will prove of interest to zoologists, especially 

 from a taxonomic point of view. Spence Bate and Henry Woodward, 

 of England, and Prof. Dana, of this country, regard the Trilobites 

 as closely related to Isopoda. Woodward homologizes thus : 



Trilobita (fossil or extinct). 



1. Eyes sessile, compound. 



2. No ocelli visible. 



3. Appendages partly oral, partly am- 

 bulatory, arranged in pairs. 



*4. Thoracic segments variable in niim- 

 ber,from six to twenty-six, free and mov- 

 able ; animal sometimes rolling in a ball. 



5. Abdominal somites coalesced, form- 

 ing a broad caudal shield (bearing the 

 branchiae beneath ?) 



6. Lip -plate well developed. 



Isopoda (fossil and living). 



1. Eyes sessile, compound. 



2. No ocelli visible. 



3. Appendages partly oral, partly am- 

 bulatory, arranged in pairs. 



* 4 . Thoracic segments usually seven, 

 free and movable ; animal soraetitnes 

 rolling in a ball. 



5. Abdominal somites coalesced, form- 

 ing a broad caudal shield, bearing the 

 branchiae beneath. 



6. Lip-plate small. 



* Incorrectly printed in Dr. Mickleborough's pamplilet, corrected from original Article 

 (Crustacea) in Encyclopaedia Britaunica (9th Edition, p. 600, Vol. VI.).— IL.W. 



