THE FAUNA OF THE ST. JOHN GROUP. 



Ill 



COMPARATIVE SIZE OF HEAD AND GLABELLA OF CT. MATTHEWI AT DIFFERENT AGES. 



Average of several. 



" " two 



" four 



Var. a. geminispinoms . 

 Average of two 



" three. 

 " four.. 

 " three. 



(( (t 



a u li 



Average of several ' . 



Length. 



Size of Cephalic 

 Shield. 



19 

 IS 

 16 

 14 

 12 

 11 

 11 



9 



8 



n 



5Î 

 4f 

 3 

 2è 



IS 



Width. 



4 



2J 

 2 



Size of Glabella. 



Length. 



9 

 8 

 8 

 6 



H 



5 

 5 

 4* 



H 



4 



3 



2è 



IS 



n 



1 



1 



Width. 



5i 

 5 



2è 

 2 



u 



1 



s 

 i 



a" 



6J0 



bo 

 a 



Proportion of the Glabella 

 to the 



Axial 

 Diameter. 





Transverse 

 Diameter. 



•25 

 •22 

 •24 

 •25 



■28 

 •26 



•3 



•27 

 •24 

 •25 



•28 



•24 



•16 



o ® 



From the preceding observations on the development of this species during its growth, 

 it will be seen that much light as to the life-history and relationship of different genera 

 of trilobites is to be gained by the study of the embryonic and larval stages, and, as I have 

 shown in my former article on the Paradoxides, it is evident that the nearer we get to the 

 embryo the more important are the phases of the trilobites, especially in reference to their 

 Ijrimitive relationship. Nevertheless, the larval stages should not be neglected, for in 

 these there are changes which, though not so momentous, are still of importance as con- 

 necting the embryonic form with the adult animal. 



B—CONOCORYPHE. 



1. — CONOCOBYPHE BaILEYI. (FlffS. 22-27.) 



Conocephalites Baileyi, Hartt. 



CEPHALIC SHIELD. 



Since Prof. Hartt originally described this species, other parts of the body have been 

 recovered, and further particulars can be given in regard to the head-shield than are con- 

 tained in his description. 



^ The measurement in the fifth column of figure.? here includes the whole length of the axial lobe, there being 

 no separate glabella. The length and width of the shield and glabella are given in millimetres. 



