446 THE TRILOBITES OF 



to the south of Girvan as well as at the typical locality of Balclatchie. The 

 mudstones have yielded the most abundant and best preserved remains of 

 trilobites obtained from the Girvan region, belonging to 31 species falling 

 under 18 genera, the facies being on the whole similar to that of the forms 

 obtained from the Stinehar limestone. 



A third horizon from which trilobites have been obtained is of Middle 

 Caradoc age, the beds being found at Whitehouse Bay and Shalloch Mill on 

 the coast south of Girvan, where they consist of calcareous shales. These 

 have yielded a special group of forms among which are Agnostus perrugatus, 

 Bohemilla sp., Cydopyge armata, 0. rediviva, Dindymene Cordai, and Dionide 

 Lapworthi. 



The next horizon lies at or near the top of the Caradoc subdivision and 

 comprises the highest beds of the Lower Silurian series in Girvan. They are 

 the well-known mudstones of Drummuck, almost identical in character with 

 those of Balclatchie, and the prolific "Starfish Bed" of Threave, both the 

 localities being in the inlier of Silurian rocks north of the Girvan valley. 

 From these beds 16 species belonging to 12 genera have been obtained. 

 Among these occur Agnostus agnostiformis and Remopleurides Colbii, the 

 last surviving remains of the two great Cambrian families of the Agnostidae 

 and Oleuidae respectively, no member of which is known to pass up into 

 Upper Silurian rocks. The Lower Silurian family of Trinucleidae is repre- 

 sented by Trinucleus seticornis and its variety T. Bucklandi, typical Upper 

 Bala forms, and Ampyjo rostratus, and Dionide Lapworthi, being only known in 

 the Girvan region from the Whitehouse horizon. This is also the last appear- 

 ance of any member of the family. 



The other genera which occur in the Lower Silurian rocks of Girvan and 



the southwest of Scotland, but which do not pass up into the Upper Silurian 



horizons, are as follows : Asaphus, Ogygia, Cydopyge (Aeglina), Stygina, 



Bronteopsis, Barrandia, Sdlteria, Bohemilla, Deiphon, Sphaerexochus, Cybele, 



.and Dindymene. 



Outside the Girvan area the only other Lower Silurian rocks that have 

 yielded trilobite remains are those of Duntercleugh and Snar Water near 

 Leadhills, Wallace's Cast on the Wandel Water near Abington, and Culter 

 Water and Kilbucho further to the east. The rocks in which they occur are 

 all of similar type, conglomerates and coarse grits with calcareous nodules, 

 associated with calcareous shales. That the rocks at the different localities 

 are on one horizon is shown by the trilobite remains which they have yielded, 

 numbering 11 species belonging to 8 genera, which are all of Lower Caradoc 

 facies and very similar to those from the Balclatchie mudstones of Girvan. 

 The horizon is proved to be probably that of the Dicranog raptus Clingani 

 sub-zone of the Hartfell group from the relation of the conglomerates to the 

 black shales of the neighbourhood where they occur. 



UPPER SILUEIAN. 



Returning to the Girvan area, the lowest members of the Llandovery rocks, 

 viz., the shelly mudstones of Mulloch Hill and Rough Neuk, localities to 

 the northeast of Girvan, have yielded the remains of 9 genera and 12 species 

 of trilobites. The next horizon is found at Woodland Point, south of Girvan, 

 in beds belonging to the Monograptus gregarius zone of the Birkhill group. 

 These rocks have yielded 14 species belonging to 9 genera, many of the forms 

 being common with those from the Mulloch Hill beds and the horizon next 

 to be considered. The next horizon is that of the Rastrites maxirnus sub-zone, 

 the highest of the Birkhill group and the top of the Llandovery rocks. The 

 beds are exposed at Penkill and in the Bargany Pond Burn to the south of 

 the Girvan Water between Girvan and Dailly. The beds there have yielded 

 J 16 species belonging to 9 genera. A few trilobites have been obtained from 

 -a somewhat higher horizon, Tarannon, in Penkill Burn. 



