THE 



GEOLOGICAL MAGAZINE. 



NEW SERIES. DECADE IV. VOL. III. 



No. V.— MAY, 1896. 



ozR,iG-i:Lsr.A.:Ej articles. 



I. — The Morphology of Triarthrus. 1 



By C. E. Beecher, 



Of Yale Museum, New Haven, Conn., U.S.A. 



(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 antennas, and its announcement by 

 Matthew in 1898, 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 specimens from the 

 abundant material in the Yale Museum. Altogether upwards of five 

 hundred individuals with appendages more or less complete have 

 been investigated ; and at the present time, it may safely be said 

 that the important exoskeletal features have been seen and 

 described. 2 



Notwithstanding the amount of information regarding the details 

 of the various organs, very little has been shown illustrating the 

 general appearance of the animal with the appendages in a natui'al 

 and lifelike position, and it is one object of the present article 

 to supply this deficiency. 



Several specimens have been lately developed which preserve not 

 only the appendages in great perfection, but also show them ex- 

 tended 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 great assistance in forming a conception of 

 general trilobite morphology. 



The dorsal view represented on Plate IX is from a camera 

 drawing based upon three specimens of about the same size. One 

 gives the entire series of legs down to the ninth free segment, with 

 the exception of the exopodites of the head, which are supplied from 

 a second individual. In the third specimen, the anterior appendages 

 are bent and irregularly arranged, while from the ninth backward 

 to the end of the pygidium they are complete and uniformly 

 extended. The figure is, therefore, a restoration only in so far as 

 representing the best portions of three individuals. 



1 Reprinted from the American Journal of Science, 4th series, vol. i, No. 4, April 

 1896, pp. 251-256. 



2 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. 



DECADE IV. VOL. III. NO. V. 13 



