TRILOBITA—HYPOPAKIA. 



257 



3. A. pisiformis Linne. (Fig. 1544.) Cambric. 



Glabella with a tubercle or posterior lobe anterior to middle and 

 with the two basal lobes subtriangular. 



Middle Cambric of St. John group of Nova Scotia. 

 4a. A. trisectus Salter var. ponepunctus Matthew. (Fig. 1545.) 



Cambric. 



Reticulation of cephalon does not reach the glabella. 

 . Upper Cambric (Bretonian) of Cape Breton. 



Fig. 1544. Agnostus pisiformis, var. Fig. 1545. Agnostus ti-isectus, var. 



a, cephalon; (^, pygidium, X4' (After ponepunctus. a, cephalon; b, a single 

 Matthew.) thoracic ring ; c, pygidium,X 2. (After 



Matthew. ) 



4^. A. trisectus var. germanus Matthew. Cambric. 



Differs from the preceding as follows: cephalon more strongly- 

 arched and smoother; pygidium without trisection of posterior 

 lobe, though faint furrows may at times be traced. 



Upper Cambric (Bretonian) of New Brunswick. 



II. MiCRODiscus Emmons. 

 Similar to Agnostus but with three or four segments in the 

 thorax, and with segmentation of the axis of the pygidium well 

 marked. Cambric. 



5. M. speciosus Ford. (Fig. 1543, c-^.) Cambric. 

 Cephalon bordered on each side by five or six tubercles. Gla- 

 bella obscurely segmented; axis of pygidium more strongly seg- 

 mented. 



Lower Cambric of New York, Quebec and Newfoundland. 



6. M. lobatus Hall. (Fig. 1543,/, </.) Cambric. 

 Glabella usually cylindroconical, and usually with no furrows 



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