108 G. F. MATTHEW: ILLUSTRATIONS OF 



across the front of the shield. Geual spines are moderately incurved and at this stage are 

 half as long as the posterior transverse diameter. 



The axial lobe of the shield is trumpet shaped, about twice as wide in front as behind, 

 where it is about one-fifth of the transverse diameter. 



The occipital ring is prominent and separated from the median lobe by a furrow ; it is 

 subtriaugular, the extremities extending forward toward the inner angles of the cheeks. 

 The summit projects backward to an elevated point which is scarcely a spine. 



The posterior margin is strongly arched, and has a distinct though not strong fold. 



The cheeks are prominent ; they are somewhat higher than the axial lobe of the shield, 

 and are tumid forward and in the outer half. The ocular ridges are still far forward on 

 the anterior slope of the cheeks, around which they arch, descending into the furrow, and 

 are lost to view about half way from the front of the cheeks. 



In small tests, such as the preceding, which bear only a remote resemblance to the 

 adult form, and which, owing to their thinness, are more liable to distortion than the suc- 

 ceeding moults, the author depends largely upon three considerations in referring them to 

 this species. There is, first, the train of succeeding sizes, which by their form and marking 

 are undoixbtedly of the species Ct. Malthewi. In the second place, there is the semi- 

 circular shield and the rudiment of the ocular ridge, which together are sufficient to show 

 that these minute tests belong to the Conocorypheans. And, thirdly, there is the consid- 

 eration of number. I think it may be safely assumed that one-third of the head shields of 

 the trilobitos, grouped by Prof Hartt ixnder the genus Conocephalites, which are exposed 

 in breaking up the shales of horizon \c at St. John, are of this species ; and of the embry- 

 onic tests found at the same locality, a corresponding number are of the above form or 

 stage. 



Second Stage. — Shield, If x 2J to If X 3 mm. Narrowly semi-circular, without 

 spines. This has the thirds of the front margin angulated, and is easily recognized as 

 related to the adult form of the species. 



Anterior viargin. — In this, beside the fold in front, the lateral thirds can be seen to be 

 slightly turned along the edge. 



The glabella is now divided from the rest of the axial lobe which forms a short promi- 

 nence in front of the glabella, and is low as compared with it. The first pair of glabellar 

 fiirrows is distinctly though lightly impressed, and the second pair can sometimes be 

 detected. The occipital ring and spine are well marked. 



The cheeks are now more spreading at the base and somewhat tumid outward and 

 forward. The two little spines at the posterior inner corner are visible. The ocular ridge 

 is higher up on the slope of the cheek than in previous stages, — being in about the posi- 

 tion of this ridge in the adult of Conocoryphe elegans. 



Sculpture. — The surface of the test when viewed with a lens appears to be finely 

 granular. 



Third Stage {Fig. Vl) — Shield, 2J X 4 mm. Narrowly semi-circular, but angulated 

 like the last, with rounded corners and without spines. 



Glabella rather wider at the posterior end than in front, but still only about one-fifth 

 of the whole width of the shield. Two pairs of furrows are now distinctly but lightly 

 impressed. The frontal lobe is still short and comparatively inconspicuous. 



