Extract

The genus Trinucleus indicates Middle and Upper Ordovician. One species is recorded from the Balclatchie of Dow Hill, Girvan (Upper Llandeillo), several species from the Whitehouse group of Whitehouse Bay and Shalloch Mill (Middle Bala), and one from the Drummuck beds of Thraive Glen and Quarrell Hill (Upper Bala).

Three species have been described and figured by Dr. F. R. Cowper Reed (1906),¹ but only one of these is completely known, T. bucklandi Barrande. This form is abundant in the Drummuck beds in all stages of growth. From the Whitehouse group Dr. Reed (op. cit.) figures and describes seven species, but as these are represented only by head-shields or pygidia, it has been considered premature to give them specific determinations and they appear as Trinucleus spp. a-g. With the aid of better material collected by the late Mrs. Gray, Dr. Reed has defined with greater precision the characters of Trinucleus sp. b. in a supplement (1914)² to the 1906 paper. T. albidus Reed, but definite knowledge of the thorax is still lacking.

The species from the Balclatchie of Dow Hill (see figure) is T. subradiatus Reed. This little trilobite is not at all rare here, but is not recorded from any other locality. Owing to the lack of well preserved material Dr. Reed's description is practically confined to the head-shield. In later works³ dealing with the head-shield (glabella and fringe) in the genus Trinucleus, Dr. Reed gives more detailed descriptions of the pitted nature of the fringe, girder of the

This 250-word extract was created in the absence of an abstract