70 TRILOBITES OF GIRVAN. 



2. Proetus latifrons (M'Coy), 1843. Plate XI, figs. 4, 4 a. 



1846. Forbesia latifrons, M'Coy, Synops. Silur. Fobs. Ireland, p. 49, pi. iv, fig. 11. 



Remarks. — The true P. latifrons of M'Coy occurs in the Lower and Middle 

 Llandovery of the Girvan area. The broad rounded triangular glabella nearly 

 reaching the anterior border, with a very narrow pre-glabellar band interposed, is 

 a characteristic feature. Unfortunately our specimens are not very well preserved, 

 and only consist of more or less imperfect head-shields. There are obscure traces 

 of lateral furrows on the glabella, and the occipital lobes are well marked. The 

 course of the facial sutures seems to agree with that of M'Coy 's type. 



M'Coy (op. cit.) described the species as follows : — " Longitudinally oval, width 

 two thirds the length ; side-lobes about one third wider than the axial lobe ; glabella 

 subtrigonal, prominent, but flattened above, length and width of the base equal ; 

 front rounded, narrower than the base ; sides with two ( ? three) short, very 

 obscurely marked cephalothoracic [lateral] furrows on each side ; neck furrow very 

 strongly marked, terminating at each end in a large flattened oblique tubercle ; 

 cheeks very prominent, triangular, nearly twice as long as wide ; eyes large, 

 reniform, close to the glabella; eye-line [facial suture] descending perpendicularly 

 to the lower margin of the cheeks, and then turns abruptly outward at its 

 extremity ; margin rather broad ; abdomen [thorax] of eleven [ten] segments, 

 those of the axial lobe [axis] terminating in prominent tubercles; side segments 

 [pleurae] compound ; pygidium semi-oval ; axial segments ten, simple ; lateral 

 segments [pleurae of lateral lobes] divided by a groove, extending rather more than 

 halfway from the margin; margin entire, even." Subsequently in 1854 M'Coy 1 

 described what he considered to be the same species from the Upper Ludlow of 

 Underbarrow, Kendal ; but the description does not quite agree with that of the 

 type, and the specimens (which are in the Woodwardian Museum) are certainly 

 different to it, though their poor state of preservation renders their characters 

 difficult to distinguish. 



The differentiation of the various Silurian and Ordovician species of Proetus 

 requires attention to minute details, and a revision of the British species is to be 

 desired. It is much to be regretted that in the majority of cases the material is 

 too poor to permit satisfactory comparison, particularly with foreign species. 



Collection. — Mrs. Gray. 



Horizon and Localities. — Mulloch Hill Group (L. Llandovery) : Mulloch Hill. 

 Saugh Hill Group (M. Llandovery) : Woodland Point. 



1 M'Coy, ' Synops. Brit. Pal. Foss. Woodw. Mus.' (1854), p. 174. 



