GENERAL REMARKS. 179 



perhaps only 24 species if we cut out two of the doubtful Trinuclnts). The 

 predominant genus is undoubtedly Trinucleus. Several rare a'id curious genera 

 only occur on this horizon, and it is remarkable that the genus Gydopijgt' is only 

 known from these beds in the Grirvan district, while in England and Wales it 

 characterises lower horizons. 



The Drummuck Group has yielded 23 genera with 27 species. We get here 

 the typical Upper Bala facies of the North of England, with Staurocephalus 

 glubiceps, Trinucleus bucMandi, PhUlipsinella parabola, etc. But some peculiar 

 genera and species occur. Most of the genera are represented by only one 

 species, and it is difficult to say which is the most abundant species. 



In the Mulloch Hill Group the number of genera has decreased to 10, containing 

 17 species. Illsenus is prominent and so is Acidaspis, but Proetus is perhaps no 

 less conspicuous. As regards the abundance of individuals the species of Illsenus 

 are undoubtedly first. 



The Saugh Hill Group contains 11 genera with 18 species. With the exception 

 of the reappearance of Bronteus after a long absence from this area the trilobitic 

 fauna much resembles that of the Mulloch Hill Group. 



In the Camregan Group there are 9 genera. Harpes reappears. There are 

 12 species present. 



The Penkill Group has only yielded 8 genera and sub-genera. Youngia is 

 peculiar to it. Illsenus is again the dominant genus and most abundant in individuals. 



The Bargany Group has only yielded one genus with one species ; and the 

 Blair, Knockgardner, and Straiton Beds three genera, each with one species. 



The most persistent genus in the Girvan area is seen to be Encrinurus, but 

 Illsenus comes second. The same species of Encrinurus, represented by two 

 varieties, is found in nearly every stratigraphical group. Many genera or sub- 

 genera, on the other hand, are restricted to one formation. This is especially the 

 case in the Whitehouse Group, which boasts six peculiar genera; and the same 

 number of genera or sub-genera is confined to the Balclatchie Group. 



