THE SILURIAN ROCKS OF SOUTHWEST SCOTLAND. 447 



From the rocks of Blair and Knockgardner between Girvan and Straiton, 

 which represent a still higher horizon, either at the top of the Tarannons or 

 the base of the Wenlock series, the following species have been obtained : 

 Catymene Blumenbachi, Encrinurus punctatus and its variety E, arenaceus, 

 Phacops Downingiae, P. Stokesi, and Proetus Stokesi. 



The genera of trilobites found in the Upper Silurian rocks of Girvan, all of 

 which made their appearance in Lower Silurian times and occur in those 

 rocks at Girvan, are, Acidaspis, Bronteus, Calymene, Cheirurus, Encrinurus, 

 Harpes, Ulaenus with its sub-genera Dysplanus and Bumastus, Lichas, Phacops, 

 Proetus, and Staurocephalus. The genera Homalonotus and Phillipsia occur 

 in the Lower Silurian rocks of the area, the former at Duntercleuch, and the 

 latter represented by Phillipsia parabola at Threave. Though these genera 

 are not represented in the Upper Silurian rocks of Girvan they pass up else- 

 where, the former to the Devonian, and the latter as far as the Carboniferous. 

 Beyond the Girvan area the only band of Upper Silurian rocks that has 

 yielded trilobites is found among the Wenlock-Ludlow rocks of the Hagshaw 

 Hill inlier of Lanarkshire. The locality is near High Broomerside on the 

 Podowrin Burn, a tributary of the Douglas Water, and the strata consist of 

 shales. These have yielded to Mr. Macconochie Calymene Blumenbachi, 

 Encrinurus sp., Ulaenus sp., Phacops sp., and Proetus Stokesi, a group almost 

 identical with that from Blair and Straiton in the Girvan region. 



It will be seen from the above that the distribution of the trilobite 

 remains is similar to that which obtains elsewhere in Britain and Europe 

 generally. The whole facies is European, even down to the forms that occur 

 in the Stinchar limestone, though the corals of that zone were shown by 

 Nicholson to be of American facies, 1 and the peculiar American gasteropod 

 genera Maclurea and Ophileta which occur in it have only been found else- 

 where in Europe in the Durness limestone. The forms have a nearer 

 affinity with those of Bohemia than those of Scandinavia and Eussia, and it 

 is evident that they belong to the same great geographical and biological 

 province. The constant association of trilobite remains with mudstones and 

 shales in the area under consideration seems to point to muddy sea-bottoms 

 not far from shore having been their favourite habitat, a fortunate circum- 

 stance, since it favoured the preservation of their moults and their dead 

 bodies for our study. 



i Op. cit., p. 95. 



