VOL. XIX. (2) 
USK TNLIER (APPENDIX) 
167 
Horizon and Locality. — Wenlock Limestone in stream by 
quarry, 300 yards North-East of Greenpool Farm. 
Remarks . — The head-shield closely resembles that of 
specimens usually referred to Proetus Stokesi (Murchison),' 
but the original description is scanty and the figure of this 
species is poor, and the type-specimen is not known. 
McCoy’s^ description was unsatisfactory, and Loven^ was 
the first to give a full diagnosis of the specific characters 
with good figures. Oiii Usk head-shields differ from the 
Wenlock examples labelled Pr. Stokesi by McCoy and 
Salter by the relatively shorter and blunter glabella, the 
stronger development of the first and second glabellar furrows 
and the larger eyes. The median ridge in the marginal furrow 
in front of the glabella which is present in our form and in 
some specimens from the Wenlock Limestone of Dudley is not 
mentioned by McCoy or Loven, nor is it shown in any of the 
figures of Pr. Stokesi, and the species is stated by Lov6n to 
have a double elevated line on the cheek, whereas in our 
specimens the line is single. A similar ridge is present 
on the cheek in Pr. astyanax Corda, as figured by Barrande and 
Oehlert."^ The segmentation of the glabella and the ornamenta- 
tion of the surface closely resemble Proetus [Phaetonides) 
rugulosus, Lindstrdm^, from the Silurian of Gotland, but no 
median ridge in the marginal furrow appears to be present, 
and the eye is smaller. Pr. astyanax, Corda, has a head-shield, 
glabella, and ornamentation much like those in the Usk 
species, as well as the concentric ridge on the cheek. 
If the hypostome and pygidium found associated with the 
head-shields in the Limestone in the Usk district are all referable 
to one species, we may remark that the former resembles that 
of Pr. concinnus Lindstr.,^ and Pr. signatus Lindstr.,^ and that 
the latter has the usual characters of Proetus and not of 
Phaetonides, which Oehlert {op. cit. p. 5) put as a sub-genus of 
1 Murchison, Silur. Syst., p. 656, t. i i, fig. 6; Reed, Mon. Girvan Trilob. (Paiaeont. Soc.), pt. 2, 
p. 79, pi. xi., figs. 10 , II. 
2 McCoy, Syn. Brit. Palaeoz. Foss. Woodw. Mus., p. 174 (Forbcsia Stokesi). 
3 Lov6n, Ofv. K. vet. Akad. Forhiindl. (1845), p. 50, t. i., figs. 3a — d. 
4 Oehlert, Bull. Soc. Et. Scient. Angers (1885), pi. i, fig. 8 : Barrande, Syst. Silur. Bohfme, 
i., p. 470, pi. xvii., fig. 22. 
5 Lindstrom, Ofv. K. Vet. Akad. Forhandl. (1885), No. 6, p. 7^, t- xvi., lig. 13. 
6 Lindstrdm, “Researches in the Visual Organs of Trilobites ” (Kongl. Svensk. Vet. Akad. 
Handl., Bd. 34, No. 8, 1901), p. 67, pi. vi., figs. 21-23. 
7 Lindstrflm, Ofv. K.Vet. Akad. Forhandl. (1885), No. 6, p. 80, t. xv., fig. 17. 
