34 SCIENCE PROGRESS. 



for a moment be supposed that we know all about the 

 Trilobites — far from it. In spite of the new and splendid 

 discoveries in America, our knowledge remains very frag- 

 mentary. But among the additional facts which are now 

 in our possession are just those which were most wanted 

 by the morphologist to enable him to give the Trilobites 

 their true place in the animal kingdom. 



As I propose to pass these new facts in review and to dis- 

 cuss their bearings, a longer retrospect mustbe dispensed with. 

 Suffice it to say that until comparatively recently zoologists, 

 relying upon comparisons with existing groups, were 

 generally agreed that the Trilobites were in some way re- 

 lated to the existing Crustaceans, but as to the nature of 

 the affinity opinions greatly differed. In 1S81, however, 

 Professor Lankester 1 connected them with the Arachnids 

 rather than with the Crustacea, basing his argument upon 

 an elaborate comparison of Limulus and certain Eurypterids 

 (both of which are undoubtedly related to the Trilobites) 

 with Scorpio. This suggestion is still a matter of contro- 

 versy, and a review of the arguments for and against would 

 take us too far from our present subject. Further, the 

 Trilobites, in spite of their prime importance in all discus- 

 sions as to the affinity of the Merostomata, play only a 

 passive part in the discussion, being dragged in, as if of 

 small account, by their specialised offshoot Limulus. We 

 may, however, at once state that the new evidence as to 

 the position of the Trilobites is entirely in favour of the 

 older view which linked them with the Crustacea. 



Returning then to this older hypothesis, two views were 

 sufficiently clearly defined to admit of discussion and criticism. 

 One sought to ally the Trilobites with the Phyllopods, and 

 relied chiefly upon the variability in the segmentation com- 

 mon to these two, and also upon the likeness between the head 

 shield of Apus and of other extinct Phyllopods with the head 

 shield of the Trilobites. The other saw in the Trilobites the 

 ancestors of the modern Isopods, and relied chiefly upon the 

 great external resemblance existing between the two forms. 

 Neither case was really very strong. The absence in the 

 1 "Limulus an Arachnid," Q.J. M. S., vol. xxi. 



