Notes on a Few Sihirian Fossils from Ayrshire. 173 



reticulate, as in A. lalage and A. hystrix. In A. tricornis, 

 Barr., the pygidiuni spines are only eight in number ; finally, 

 there are eight also in A. mira, but the arrangement of them 

 is again different from any of the preceding. 



So far as I have been able to ascertain this is an un- 

 described form, with which I have much pleasure in associat- 

 ing the name of Mrs Gray. 



Loc. and Horizon. — Balcletchie, south-east of Girvan, in 

 rocks of Silurian age ; exact horizon not yet determined. 



Genus Cheirurus — Beyrich, 1845. 



(ijber. Bohm. Trilob,, p. 5.) 

 Cheirurus trispinosus — J. Young. 



C. trispinosus, Young. Proc. Nat. Hist. Soc. Glas., i., pt. 1, 

 pp. 169-171, t. 1, f. 4-6. 



Ohs. — This species was established by Dr John Young for 

 a peculiar form with the cervical fold prolonged backw^ard 

 into a spine, and curved in a similar manner to the genal 

 spines. Mrs Gray now has in her cabinet a more perfect 

 specimen than that figured by Dr Young, with the three 

 spines or remains of them in position. That on the left 

 (when looking down on the head from behind forwards) is 

 perfect, but of the right one only about a third is preserved, 

 whilst the middle spine is broken off close to its attachment 

 to the cervical fold. The entire head, as far as preserved, is 

 densely covered with small unequal tubercles or papillae. 



Loc. and Horizon. — Penkill, south-east of Girvan, in rocks 

 of Silurian age ; exact horizon uncertain. 



Genus Agnostus — Brongniart. 

 Agnostics trinodus, Salter. 



A. trinodus, Salter, Mems. Geol. Survey, 1848, ii., pt. 1, p. 

 351, t. 8, f. 12 and 13. A. trinodns, Salter, Mems. Geol. 

 Survey, 1864, Dec. xi., No. 1, p. 8, t. 1, f. 8-10. 



Ohs. — The specimens of this species found by Mrs Gray 

 consist of disconnected heads and pygidia. In the former 

 the slight lateral indentation of the glabella is visible, and in 



