﻿36 BRITISH FOSSIL CRUSTACEA. 



of obtaining a correct idea of the general form of the body and the position of the 

 appendages, entire specimens, such as the foregoing, are invaluable, we must not, there- 

 fore, omit to study carefully the far more numerous detached portions which have been 

 met with, and the separate parts of appendages, as they not unfrequently offer details less 

 clearly seen in the more perfect remains. 



We have only to turn over the first seven plates, and especially to note the beautiful 

 series of appendages figured in Plate VII, 1 to be convinced of their great value, not only 

 in enabling us to complete our knowledge of the anatomy of these very ancient Crustacea, 

 but also accurately to ascertain their proportions. 



The Carapace.- — At the period of the publication of Messrs. Huxley and Salter's 

 Monograph the only examples of the carapace of this genus were in the collection of 

 Lady Kinnaird. 2 One of these curious flattened plates is figured at plate iii, fig. 1, of 

 that work, which led to the conclusion that the head-shield was trapezoidal in form when 

 perfect (op. cit., p. 11) ; but the tolerably perfect detached head figured on Plate I, fig. 2, 

 shows a decidedly semicircular front, as is also well seen in the head of the nearly entire 

 but smaller specimen (Plate II, fig. 1), in which the posterior angles are also considerably 

 rounded off where the carapace is united to the thoracic somites. 



The organs of the Head. — In speaking of the paired appendages of the cephalon, we 

 shall observe the same order as is given for the restored figures of Pterggotus anglicus, in 

 the explanation of figs. 1, and 2, Plate VIII. 



The Eyes. — Both the detached head on Plate I, fig. 2, and that on Plate II, fig. 1, 

 exhibit the large convex marginal eyes upon the antero-lateral border of the carapace ; but 

 I am unable, in these or in any of the other specimens which I have examined, to detect 

 the facetted surface of the cornea. Mr. Salter, however, has satisfactorily made them out 

 in the specimen from Lady Kinnaird's cabinet, and says (Mon. cit., p. 68.) — " The 

 lenses are rather large, about eight rows in one tenth of an inch, and in this specimen are 

 rliomboidal rather than hexagonal, at least in arrangement ; this may be due to pressure 

 only." (See ' Survey Mon.,' pi. iii, fig. 1, la, and 15.) Prof. Huxley observes (op 

 cit., p. 20) — ''Notwithstanding the peculiar character of the markings upon the corneal 

 surfaces of these eyes, I wait for better evidence than I have hitherto met with, before 

 deciding that they were really compound, and that these markings indicate corneal 

 facets." 



No ornamentation can be detected on the head-shield of the smaller specimen (Plate II, 

 fig. 1), but the surface of the larger detached carapace (Plate I, fig. 2), when magnified, 



1 Copied (with the exception of fig. 4) from plates vi and vii of Messrs. Huxley and Salter's Mono- 

 graph on the Euvypterida (18.59), from Mr. C. R. Bone's very excellent figures. 



2 Although these and other specimens are spoken of in the 'Survey Monograph' as "from the col- 

 lection of Lord Kinnaird," I am informed by my friend Mr. Powrie that it is her ladyship who is especially 

 devoted to palaeontology ; and I therefore beg leave to associate her name with these interesting specimens 

 in the collection of which she has taken so much interest. 



