NIAGARA GROUP. 
317 
From the similarity of our specimens with the figure of Murchison, I have been induced to 
refer them to the same species, though there may still be some doubt as to absolute identity. 
Neither of the specimens enables me to count ten articulations in the thorax; eight only being 
visible in the folded specimen, and only the same number in the flattened and somewhat 
mutilated specimen in shale. The most striking peculiarity of the species is in *the cephalic 
shield, which reminds one strongly of the Cephalaspis. 
Fig. 13. An individual in soft shale, with the crust partially exfoliated. 
Fig. 14. An individual in limestone, partially folded, and having the buckler imperfect. 
Position and locality. In the shale, and in the thin layers of limestone associated with the 
same, at Lockport. 
677. 1. BEYRICHIA SYMMETRICA (». sp.). 
Pl. LXVII. Fig. 16. 
Compressed, smooth (or very finely granulated) ; dorsal side straight; base slightly emar- 
ginate; extremities nearly similar; a fold or border extending entirely around the ventral 
edge; on each side, equidistant from the centre, a lateral tubercle extends from the dorsal 
margin to the ventral edge on each side of the emarginate centre. Within these tubercles or 
ridges is another ridge, commencing on the dorsal margin, and running nearly parallel to the 
lateral ridge, curving around and again reaching the dorsal margin, leaving a deep central pit. 
The groove between the two ridges becomes wider and deeper, receding from the dorsal margin, 
owing to the increasing elevation and expansion of the lateral ridges. 
This species approaches in some degree to the B. complicata of Salter ; but the lateral 
tubercles only unite on the ventral edge, while the central one is very marked and distinct, 
being in fact a continuous ridge from the dorsal margin, reaching nearly across the shell, and 
curving suddenly backwards. The two extremities are so nearly symmetrical, that no appre¬ 
ciable difference can be noticed. The lateral tubercles or ridges are often so much expanded as 
to prevent the ventral margin from being seen when looking directly upon the specimen. 
Fig. 16. Specimen natural size and enlarged. 
Position and locality. This species occurs with the following upon the calcareous layers in 
the Niagara shale. It is extremely minute, and not readily distinguished on a cursory exami¬ 
nation. 
678. 2. CYTHERINA SPINOSA ( n. sp.). 
Pl. LXVII. Figs. 17-22. 
Minute, subreniform; dorsal side straight, scarcely so long as the greatest length of the 
shell and slightly pointed at one extremity j external surface granulate; a sharp spine with the 
