268 



In all the Merostomata both those belonging to the Eurypterida and to the 

 Xiphosura ('i.e., the long and the short-bodied divisions, represented by Pterygotus 

 and Limulus) the appendages are confined to the mouth ; or, where other organs 

 exist, they are always modified to act either as respiratory or reproductory 

 organs. 



The appendages in Dr. Mc Cullough's specimen, however, cannot be referred 

 to either of these functions, but are clearly the basal points of organs specially 

 differentiated for locomotion, and, so far as we are able to judge by comparison, 

 they are most probably the basal joints of true running or walking limbs, rather 

 than of swimming feet, although some of them we may conclude (on the evidence 

 of the fragments of linibs in Sketch No. 10, Figs. 2 and 3) were provided with 

 chelate terminations. 



The basal joint of these walking limbs is 3 inches in its greatest length ; 

 it is only 2 lines in breadth at the proximal end but increases rapidly to 16 lines, 

 its greatest breath, at the distal extremity. The legs must have been very robust 

 as the section of one, exposed on the border of the fosil, shows it to have been 

 9 lines in thickness. The under surface of the limbs and sternum appear to have 

 been smootli and destitute of ornamentation of any sort ; whilst the upper sur- 

 face of each limb was evidently covered with prominent rounded tubercles irre- 

 gularly dispersed over each joint. This is shown by the detached limbs seen in 

 Sketches No. 10, by the displaced limb seen at e, e, sketch 9, Fig 1 A., and is 

 proved by an examination of the before-mentioned section of basal joint preserved 

 in situ (Sketch No. 9, Fig. 2 B. x) where the upper surface is seen to be distinctly 

 tuberculated. From the preservation of a second pair of appendages (o, o,) 

 belonging to another segment posterior to, but apparently like that of which both 

 the upper and under surfaces are preserved, we perceive that the fossil forms 

 part of a Crustacean having its body composed of a series of segments of nearly 

 equal size, each segment being furnished with a pair of ambulatory or other 

 appendages for the most part adapted for walking ; in other words resembling a 

 modern Isopod. 



Among the Idoteidce the form presents itself which appears to us most 

 suitable for illustration of this fossil remain, namely, the Arcturui fldotea) 

 Baffini, Westwood (figured in the annexed woodcuts.) 



