NIAGARA GROUP. 



313 



those from the buckler, and which pass entirely around the posterior margin of the pygidium, 

 occupying two-thirds of its width. I have never yet seen a specimen having the outer crust 

 preserved entire, to the extremities of the articulations ; but some fragments of it usually 

 remain to show its original extent. 



The groove extending along the lateral articulation commences near the upper margin : 

 thence bending downward, and running along near the centre, it gradually approaches the 

 lower margin, and terminates at the apex on the lower margin. 



Several magnificent specimens of this species have been found at Lockport, two or three of 

 which are each about seven inches long and five broad. I have rarely seen individuals less than 

 five inches in length ; and in all the collections made by different individuals at this place, I 

 have seen only two small ones of about three inches in length. 



PLATE LXIX. 



Fig. 1. A large individual of this species, as perfect as usually found of this size. The eye tu- 

 bercles are crushed, and so much mutilated that their form is not well preserved. 

 The extent of the scabrous outer crust can be inferred from the patches still remaining. 



PLATE LXX. 



Fig. 1 a. The head of an individual smaller than the preceding, in which the form of the eye 



tubercles is more distinctly preserved, as. well as the form and direction of the lateral 



lobes of the glabella. 

 Fig. 1 b. The under side of the head and several articulations, showing the clypeus attached 



below the front of the glabella. This specimen is from the collection of Col. Jewett, 

 Fig. 1 c. A fragment of another specimen, showing the impression left after the removal of the 



clypeus. 

 Fig. 1 d. The under side of the glabella, where the clypeus is removed. 

 Fig. 1 e. Profile of the buckler, showing the elevation of the eye in a specimen where it is very 



well preserved. 

 Fig. 1 /. A fragment of the glabella and base of the buckler. Fragments of this kind are very 



common, and, with the pygidia, are the only portions found in some localities. 

 Fig. \ g. A. pygidium of a specimen of medium size, showing more pointed terminations of the 



articulations. 

 Fig. 1 A. A smaller pygidium with the terminations broken. 

 Fig. 1 i. A young individual of this species, having the base of the buckler broken. The caudal 



extremity presents some slight deviations from the ordinary appearance of larger 



specimens, but appears in the two small individuals seen, and in a separate small 



pygidium fig. 1 h. 



Position and locality. In the shale at Lockport and Rochester, at Sweden in IMonroe county, 

 and at Wolcott in Wayne county. Perfect specimens have been found only at Lockport. The 

 most perfect specimen I have seen is in the collection of the Albany Institute. The matrix is 

 also preserved with it, showing the cavities of the eyes, from which the form has been taken 

 in the figure of a head, PL 70, fig. 1 a. 



[Paleontology — Vol. ii.] 40 



