INTRODUCTION. 1 1 



of their author. M'Leay, too, on this occasion, as he lias often clone clscwhei'c, confounds the 

 ideas of analogy and affinity, the first distinction of which in England is justly considered 

 as his greatest and generally acknowledged merit. Another English author, however. Dr. 

 Buckland, had not long before (183G) already explained the same subject with much genius 

 and vigour. He believes that Scrolls, Limulus, and Bramkipus are the three genera of living 

 Crustacea, to which the Trilobites are most nearly related, and he founds his comparison 

 on the resemblance of general form in the first, the structure of the cephalic shield in the 

 second, and the structure of the feet and nature in the eyes in the third. How far these 

 assumptions are well founded, we shall subsequently investigate. 



I will not here touch at greater length upon the several observations of contemporary 

 writers, as of Hönighaus, Bronn, H. v. Meyer, Hünefeldt, J. V. Thompson, Sowerby, Jukes, 

 Esmark, Green, and Harlan, but will proceed to some more recent, more elaborate, and more 

 important works, which form the conclusion of the researclies hitherto made. Hiesinger, 

 in his General View of the Swedish Trilobites (1837), the first of these publications, 

 follows Dalman's example exactly, and gives but few new facts. Quenstedt's* statement in 

 Wiegmann's ' Archiv' (1837, 1), deserves greater attention, especially on account of the import- 

 ance which was here first attached to the numerical proportions in the difi"erent divisions 

 of the body, particularly of the trunk. I must, however, dispute the correctness of the 

 author's representation of the eyes, of which he assumes two types, and also his assertion 

 that a division of the group into genera is not yet necessary. With regard to the latter 

 point, it should be remembered that the object of the descriptive natural sciences consists by 

 no means in the mere registering of natural bodies, but involves the unveiling of those 

 differences, subordinate one to another, by which nature has changed the original simple 

 type into so many various forms. Having once correctly recognized such distinct degrees 

 of modification, and having made out the characteristics of these modifications, we then 

 consider them as genera, or speaking generally, as groups to which we give special names, 

 in order to remind us of the peculiarity in the modification of the fundamental type. For 

 this and for no other reason is it that we give names to the groups, intending simply 

 to facilitate the interchange of ideas and experiences, just as the use of coin facilitates 

 commercial intercourse. Quenstedt's predecessors knew this quite as w-ell as his successors 

 have appreciated it, and made it their object to establish well-founded genera. Boeck onl)^ 

 attempted to indicate these (in Keilhaus 'Gaea Norwegica,' 1838), reserving for himself 

 the particular description in a ' Monography of the Trilobites,' which has long been an- 

 nounced, but which has not yet made its appearance. Emmerich in this, howevei", has 

 anticipated him, succeeding Quenstedt as assistant at the Mineralogical Museum at Berlin, 

 and likewise following in the footsteps of the latter naturalist, and choosing the Trilobites as 

 the particular object of his studies. In his carefully executed work (Diss. Inaug. Berol. 

 1839) the general part is certainly not much enriched by new facts or views, but the special 

 part is written with a careful investigation of the manifold synon)'ms, and built on the gene- 



* I believe that I was the occasion of this statement. During a visit to the !Mineralogical 

 Museum at Berlin, at which ]M. Quenstedt ^^as tlien assistant, I explained to him my views respecting 

 the Ti-ilobites, their structure and their affinities, and laid particular stress on tlic importance of the 

 numerical proportions. The statement alluded to was published a few months subsequent to that 

 conversation. 



