221 



Horizon ond locality. In bituminous limestone bed of the Band C. 36, 

 at Me Adam shore, Escasonie, Cape Breton. 



A singular condition of preservation of the test of this species is the 

 rarity of remains of the thorax. Among two dozen heads and three dozen 

 tails of this species, only one joint of the thorax was observed. 



Larval characters. The reticulation or furrowing of the cheeks, which Larval 

 is so obvious a character of adult head-shields, becomes less and less pro- characten; - 

 nounc d in the small heads, and disappear in minute ones. Faint furrows 

 are impressed at the sides of the main lobe of the glabella, opposite the 

 median tubercle, showing a somite here to which this tubercle belongs ; 

 the examples are l^mrn. long, in which this is apparent. 



A pygidium mm. long, shows a comparatively short rachis of two 

 segments of which the anterior is dominated by a low ridge-like tubercle ; 

 no true anterior lobe, such as is found in adult shields, can be detected 

 at this stage. The posterior lobe, by faint tubercles at the sides is shown 

 to be composed of at least two somites, yet the trisected condition of the 

 rachis is already apparent. 



Mut. GERMANUS. 



Bull. Nat. Hist. Soc. of N. Brunswick vol. iv. p. 279. 



This interesting form has many points of resemblance to A. trisectus, Mutation 

 and is of nearly the same size, but yet is not trisected on the posterior pe " 

 lobe of the rachis of the pygidium. This form and mut. ponepunctus 

 sometimes occur scattered over the same surface of rock, but more fre- 

 quently are distributed on different surfaces. The smoothness of the slopes 

 of the shields and the absence of trisection in the posterior lobe might 

 lead one to think it a different species from mut. ponepunctus and from 

 A. trisectus, type, but the tubercle at the end of the rachis of the pygidi- 

 um, peculiar so far as the author knows to the Cape Breton forms, leads 

 one to think they belong to one species. 



Horizon and locality. In Band (C. 36) at Escasonie shore, East bay, 

 N.S. 



Since writing the above I have received a letter from Prof. J. E. Marr, Compared 

 of St. John's College, Cambridge, who has had the examples of A. trisec- 

 tus, in the Woodwardian Museum examined, and also those of the Geolo- 

 gical Museum in Jermyn street, London ; on none of these is there any 

 trace of a tubercle at the extremity of the mid- lobe of the pygidinm. 

 This indicates a closer relationship between the two Canadian forms than 

 is borne by either of them to tho type, though the apparent difference 



