THE FAUNA OP THE ST. JOHN GROUP. 67 



other end is plain ; this distinction may be used for the purpose of locating the characters 

 of the inner surface of the test, as seen on the mould of the valve. 



The centre of the valve is marked by a distinct circular depression, apparently a per- 

 foration of the test : from this point a faiut median furrow extends toward the tuberculated 

 end, where it fades ou.t in the shallow pit existing at that end of the valve ; this pit is larger 

 than the circular depression at the centre of the vah'e, but differs from it in having no 

 defined margin ; beside this larger pit, but nearer to the margin of the valve, is the tubercle 

 above referred to ; it is low, somewhat pinched up at the sides, and elongated in the direc- 

 tion of the larger axis of the valve. The slope of the sides of the valve near the margin 

 is nearly vertical, and the marginal fold is very feeble and obscure. 



The surface of the vah'e is granulated, but the granulations are more distinct on the 

 inner than the outer surface ; the inner surface is more brilliant than the outer. 



This Primitia resembles in form and size the Silurian P. transiens, Ear. ; its apparently 

 perforated disc recalls another Bohemian species, P. perforata, Bar. ; in this species the per- 

 foration and tubercle are situated near the hinge line, but in ours near the axis. 



Lengih, 3i mm. Width, 2 mm. 



Horizon and Locality. In the conglomerate-limestone baud, Div. l.r', at Porter's Brook, 

 St. Martin's. 



IX.— TRILOBITA. 



AGNOSTUS, Brong. 



Ten species and varieties of this genus are known from Division 1. They exhibit 

 several modifications of the generic type, and may be arranged as follows : — 



1. Small species, with prominent pygidial rachis and with large glabella, having a 

 wide fore lobe, (compare A. rex, Barr., and A. regies, Sjogr.) — one species in Div. I.e. 



2. Species with smooth test, smaller fore lobe to the glabella, and wider side lobes to 

 the shield, (compare A. fallax, Linrs.) — three species in Div. \.c, and two varieties in 

 Div. l.d. 



3. Small species of high contour and obsolete or obsolescent fore lobe to the glabella, 

 (compare A. hrevifrons, Ang.) — two species in Div. l.d. 



4. Large species, having a thin, granulated test, (compare A. punctuosus, Ang.) — 

 two species in Div. l.d. 



The A. lœvigatus gToup, with obscure glabella and pygidial rachis has not yet been 

 recognized in the Cambrian rocks of the Acadian region. 



ActNOSTUS REGULUS, u. sp. (Plate YII. Figs. l<i. I) and c) 



Elongate-elliptical, with straight sides and semicircular ends. 



Cephalic shield, elongate semi-elliptical with straight sides ; posterior contour broken 

 by the projecting glabella and narrow occipital riag. The width and length of the head 

 shield are nearly ec|ual. The dorsal furrow is distinctly, but not deeply impressed. The 

 marginal furrow and fold are sharply defined, and the latter diminishes toward the pos- 

 terior angles of the shield. 



