MUSEUM OF COMPARATIVE ZOOLOGY. 209 



adopted in accordance with tlie advanced views of Milne-Edwards, 

 Gegenbaur, Lankester, Van Beneden, Yerrill, and other authors. 



The more conservative zoologists consider the group as an order or 

 sub-class of the Crustacea, while others view it as a sub-class of the 

 Arachnida.* Professors A. Milne-Edwards,t Gegenbaur, t and E. Ver- 

 rill § consider the group as a class of the Arthropoda, placing it after the 

 Crustacea and preceding the Arachnida in the scheme of classification. 

 With this course we are in accord. || 



The following arrangement is made to express the view of the rela- 

 tions of the different orders forming the group. 



ARTHROPODA. 



Class PCECILOPODA. 



Sub-class Merostomata. Sub-class Faljeabje. 



Order Xijihosura. Order Trilobita. 



Order Eurypterida. 



PCECILOPODA. Arthropods with the cephalic appendages sub- 

 serving the function of manducation. 



Sub-class Mekostomata. Pcecilopods with ocelli in addition to 

 compound eyes, all the limbs serving as mouth organs, the mouth pro- 

 vided posteriorly with a metastoma. 



Order Xiphosicra. Mouth furnished with a small hj'postoma and 

 six pairs of appendages. Posterior segments of the body more or less 

 free, and all bearing branchiae or reproductive organs. 



Order Eurypterida. Mouth furnished with five pairs of appendages. 

 Two anterior free segments, bearing branchiae or reproductive organs. 

 Other free segments devoid of appendages. 



Sub-class PALiEAD.E. Pcecilopods with numerous thoracico-abdomi- 

 nal appendages. Eyes compound (when developed). Ocelli unknown. 



* Professors Ed. Van Beneden, E. Ray Lankester, Introduction to Gegenbaur's 

 Elements Comp. Anat., English ed., 1878. 



t Ann. des Sci., XVII., 1872. 



X Elements Comp. Anat., English ed., p. 230, 1878. 



§ Classification of Animals, Yale College, 1879. 



II " It is by no means desirable that students should be taught to accept any one 

 scheme of classification as finite. They should be taught to look upon these schemes 

 as the condensed expression of an author's views, — as the epitome of his teaching, 

 facilitating the recollection and comparison of conflicting solutions of the vast series 

 of unsolved problems of morphology. " Prof. E. Ray Lankester. 



VOL. VIII. — NO. 10. 14 



