24 Fossils of the Utica Slate, 



1847. Prof. James Hall in vol. i, JPal. JV. Y, p. 251, in describing 

 Calymene ( Triarthrics) JBecki says : 



" There is still some little difficulty in determining the number of 

 articulations of the thorax, since the greater number of specimens are 

 imperfect ; and in a single large specimen there appear to be fourteen 

 or fifteen. This fact indicates an increase in the number of thoracic 

 rings with age, a character which Emmrich has given of Olenus." 



1852. Prof. Barrande^ in noticing the above remarks says. 



" In a previous passage (p. 237) relating to the same species [ Caly- 

 mene {Triarthrus) Becki]. J. Hall rei^aids it as having thirteen seg- 

 ments. The extent of the supposed variations in the number of thoracic 

 elements wall then be from thirteen to fifteen, this last limit, however, 

 is given with some doubt. The numerous figures given by the author 

 elsewhere, show that the materials at his disposal were incomplete. 

 It seems to us then, before definitely admitting a progressive devel- 

 opment, it is necessary to await new documents ; as for the character 

 attributed to the Olenus by Emmeich it comes from an error of 

 observation." 



1857. Prof. E. Billings comparing Triarthrus Becki with Triar- 

 thrus spinosus, which he then described as having thirteen thoracic 

 segments, says 



" In a well preserved specimen of Triarthrus JBecki in the museum, 

 there are distinctly fifteen segments in the thorax, and five in the 

 axis of the pygidium, so that if these two species be congeneric, the 

 number of articulations in the genus must be a variable character." 



1872. Prof. J. Barrande gives Triarthrus Billingsi as having 

 sixteen segments in the thorax (table, p. 116, vol. i, Pt. ii, Syst. 

 Sil. Boheme). 



Metamorphoses of Triarthrus Becki. 



As the metamorphoses, or all changes experienced by a trilobite 

 during its life, are given of Triarthrus Becki as far as known, the 

 following quotations from Prof. J. Barrande's exhaustive discussion 

 of the metamorphoses of the trilobites ^ are taken as a basis, as his 

 work is the foundation upon which investigations in this line of re- 

 search must be based : 



" Whatever may have been the real extent of the modifications of 

 form undergone by the trilobites from their leaving the egg to the 

 adult age, it is clear that we can find traces of the transformation 

 of their solid envelope, only ! All the variations relating to the soft 

 parts, such as the feet, antennae, etc., which play so important a part 



^ Systeme Silurien de la Boheme, vol. i, p. 259. 



Rdpori of Progress, Oeol. Survey, of Canada, p. 340. 1857. 

 ^ Loc. cit., I, pp. 281, 282. 



