114 



G. F. MATTHEW: ILLUSTRATIONS OF 



stronger, as is also the posterior, but the occipital ring preserves the same triangular form 

 as in the stage last described. 



Sculpture. — Except the anterior marginal fold, which is minutely granulated, the sur- 

 face of the test at this stage appears scabrous under the lens. 



Shield 4X6 mm. {Fig. 35.) — A shield of this size has been found which has some 

 peculiar features. The glabella is conical, narrowed in front and with three sets of distinct 

 furrows, as in C. elegans, and, like some shields of this species, it has raised ridges across 

 the glabella between the furrows. But the eyelobe, cheek and anterior marginal fold are 

 such as are found to characterize C. Baileyi. The surface is scabrous. 



Shield "T X 14 mm. {Fig 2*7) — The intermediate sizes between this and the preced- 

 ing have not been recovered, but at this stage the shield has nearly attained the proportions 

 of the mature form. The glabella has more distinctlj^ converging, straight sides than the 

 last, and also possesses the sub-quadrate front which is found in most of the mature heads. 

 All the furrows are distinctly impressed. The occipital ring is narrowed, and its spine, 

 or tubercle, placed half way from the front. Respecting the succeeding sizes of this sj)e- 

 cies, there is little of moment to be said : both glabella and cheeks continue to increase 

 in width at the base, and a greater amount of variation appears in the distinctness of the 

 furrows on the glabella. 



The following table will more clearly show the variation in the form of the shield and 

 the relative proportions of the glabella during growth. The figures given for the small 

 tests are only rough approximations : — 



COMPARATIVE SIZE OF HEAD AND GLABELLA OF C. BAILEYI AT DIFFERENT AGES. ' 



Var. a. {Fig. 23) 

 Like Fig. 22 . . . 



Var. o. 



Fig. 27 

 Fig. 35 



Fig. 26 



Fig. 25 



Well rounded. 



/Somewhat flattened 

 \ and spread. 



Well rounded. 



Rather flat and wide. 



Somewhat flattened. 



Narrowed. 



Diagonally narrowed. 



Narrowed. 



Flattened. 



Shortened. 



r Flattened and cheeks 

 \ narrowed. 



Somewhat flattened. 



' The measurements in this table are in millimetres. 



