6. THE MORPHOLOGY OP TRIARTHRUS* 



(PLATE IX) 



MOST of the recent advances in the knowledge of trilobite 

 structure have come from the study of Triarthrus. Since 

 Valiant's discovery of the antennae, and its announcement by 

 Matthew in 1893, the writer has published a series of papers 

 on the detailed structure of this trilobite. Much time has 

 also been spent in carefully working out the numerous speci- 

 mens from the abundant material in the Yale Museum. 

 Altogether upward of five hundred individuals with append- 

 ages more or less complete have" been investigated, and at 

 the present time it may be safely said that the important 

 exoskeletal features have been seen and described, f 



Notwithstanding the amount of information regarding the 

 details of the various organs, very little has been shown illus- 

 trating the general appearance of the animal with the append- 

 ages in a natural and lifelike position, and it is one object 

 of the present article to supply this deficiency. 



Several specimens have been lately developed which pre- 

 serve not only the appendages in great perfection, but also 

 show them extended and disposed in a very lifelike manner. 

 No new structural points are here brought out, yet the 

 representation of the complete animal serves as a summary 

 of present knowledge, and also gives a definite picture of 



* Amer. Jour. Sci. (4), L, 251-256, pi. viii, 1896. Reprinted in Geological 

 Magazine (London), dec. iv, III, 193-197, pi. ix, 1896. 



t The more important literature relating to the structure of the genus 

 Triarthrus is given at the end of the present article ; numbers in the text refer 

 to this. 



