360 SYSTEMATIC POSITION OF THE TRILOBITES. [Aug. 1895, 



Judging from the occurrence of Protocaris MarsMi (an early 

 Apus) with Olenellus in Lower Cambrian rocks, the ancestors of 

 Apus must have been contemporary with those of the trilobites, 

 and such a form as Protocaris may have given origin to the Phyllo- 

 carida of the Palaeozoic rocks, which they somewhat resemble, save 

 that the latter have a much smaller number of segments. The great 

 number of segments in Apus and in some trilobites was a very 

 annelidan character. 



Dr. J. W. Gregory thought that all palaeontologists would be 

 glad that appendages in trilobites had been found and described by 

 so careful a worker as Dr. Beecher. He thought that the new 

 facts described confirmed the view of the close alliance of trilobites 

 with the phyllopods for which Mr. Bernard had contended, but he 

 still doubted whether its descent from an annelid was sufficiently 

 proved. The limbs of Apus seemed to him more to resemble 

 arthropod appendages than annelidan parapodia. 



Mr. E. T. Newton also spoke. 



The Author stated, in reply, that there seemed to be no escape 

 from the conclusion that the immediate ancestors of Apus (and 

 consequently of the trilobites) possessed between 60 and 70 segments ; 

 that is, they were annelids, further, what we now know of Apus 

 and of the trilobites enables us to trace step by step the course of 

 the transformation of the chaetopod into the crustacean. 



It was not contended that Apus was an ancestral form of the 

 trilobites, only that in its enormous number of trunk-segments, and 

 in their cylindrical form, Apus had retained primitive annelidan 

 characters which the trilobites had lost. On the other hand, as- 

 was shown in the paper, the trilobites (as represented by Triar- 

 thrus) had retained annelidan characters which had been lost in 

 Apus. The position adopted by the Author in his previous paper 

 was now fully confirmed, — the trilobites were to be regarded as fixed 

 stages in the development of Apus from a chaetopod, specialized for 

 a creeping manner of life. 



