Vol. 52.] FAUNA OF THE KEISLEY LIMESTONE. 409 



possesses all the characters of Billings's species l which occurs in the 

 Quebec group, except that the axis in our specimen is rather shorter 

 than in his figure, and therein approaches Agn. tardus of Barrande. 2 

 The ornamentation of the surface, of which Billings says {he. cit.) 

 that one specimen showed indications, is very clearly exhibited, and 

 consists of fine reticulating or undulating raised lines or fine 

 wrinklings on the zone of the lateral lobes ; the striae run more or 

 less concentrically to the margin of the pygidium. The remainder 

 of the test is smooth. 



The specific differences of this species from Agn. tardus (see 

 Billings, he. cit.) are : — (1) The elongated central tubercle on the 

 axis is elevated at its abrupt posterior extremity to twice its height 

 at its anterior end. 



(2) The zone of the lateral lobes is ornamented by fine wrinklings 

 or raised lines. 



Tkintjcleidj«;. 

 AiTPTX binodulosus, sp. n. (PI. XXI. fig. 1.) 



The specimen in the Woodwardian Museum which had been 

 assigned to Eorbes's species A. tumidus cannot, in my opinion, be 

 allowed to remain in that species for the following reasons : — 

 (1) The cheeks unite with the glabella in front of the middle of its 

 length ; (2) at the base of the glabella are two distinct circular 

 nodules or lobes, which occupy nearly its whole breadth, so as 

 almost to touch each other in the centre. 



There is another smaller specimen of this new species in the 

 Harkness collection at Carlisle. 



The glabella is almost lanceolate in shape, but is truncated 

 abruptly behind by the distinct neck-furrow. In front the glabella 

 tapers gradually into a grooved spine (broken off short in our 

 specimen). 



The glabella is most convex from side to side at the level where it 

 becomes free and projects in front of the cheeks ; from its posterior 

 end to the base of the spine it is very gently and regularly convex. 

 A faint keel runs longitudinally down its centre, and at the base 

 of the glabella lie the pair of circular flattened lobes or areas, one 

 on each side of the keel. These circular areas or lobes scarcely 

 rise above the general level of the glabella at this part, but extend 

 nearly across its whole breadth, giving it a very characteristic 

 appearance. 



The cheeks are triangular, somewhat swollen and distinctly 

 marked off by shallow axal furrows from the glabella, with which 

 they unite at a point rather in front of the middle of its length. 

 Near the anterior end of each axal furrow and in its course there 

 lies a small but deep pit. The genal angles appear to have been 

 produced into rounded spines. 



The neck-segment is narrow, but distinctly marked off from the 



1 Billings, Geol. Surv. Canada, Palaeozoic Fossils, vol. i. (1865) p. 297, fig. 288. 



2 Barrande, ' Syst. Sil. Boheine,' vol. i. (1852) p. 913, pi. xlix. 



2f2 



