XIX.— Some New Girvan Trilobites

Abstract

Introduction. The main purpose of the present paper is to describe a few new species of Proetus and the hitherto unknown hypostome of Cybele nicholsoni Reed. Proetus is probably represented by more species than any other trilobite genus in the Ordovician and Silurian rocks of the Girvan district. There is, however, a great paucity of individuals of the various species with the exception of Proetus girvanensis which is abundant in several exposures of the Drummuck Group in Lady Burn. Few Proetids have been recorded from exposures in the Balclatchie Group; one from Dow Hill, one from Balclatchie, and another from Balclatchie placed in Cyphaspis but perhaps referable to Proetus. Three species of Proetus recently obtained from the latter locality possess distinctive features which it is desirable to place on record. Several small examples of Proetus have been described and figured from the Newlands exposure in the Saugh Hill Group. Two large pygidial external impressions found at this locality are referable to Proetus. Opportunity is also taken to discuss the nature and function of the “Verschlussfurche” interlocking furrow, which has been observed on the ventral surface of several specimens of Phacops ( Phacops ) elliptifrons Sars & Boeck. A defective head-shield with a portion of the thorax partially enrolled. The head-shield is semiannular in contour, the free cheeks extend to such an extent posteriorly that the cephalic length is only slightly more than one half of the total length of the head-shield including the genal spines. The glabella in relationship to its length This 250-word extract was created in the absence of an abstract The thanks of the author are due to Professor T. Neville George of Glasgow University for giving photographic facilities and for other generous help, and to Dr. A. Lamont for assistance during the progress of research.