CATIADOCIAN CYSTIDEA FROM GIRVAN. 475 



^ 466. Locality. — Dr Jaekhl (1899, p. 235) says " angeblich Schottlands ? vielleicht 

 Siid-Wales," aud then names the species " angliciis." So far as I am aware the species 

 does not occur in Scotland or Wales or England, but, as explained in § 468, comes from 

 Bardahessiagh, co. Tyrone, Ireland, and probably from one of the localities numbered 

 2 and 3 in W. H. Baily (1878), "| mile N. of slate quarry R. C. Chapel, 2^ miles 

 N. of Pomeroy." 



^ 467. Horizon. — The matrix of the known specimens is a micaceous sandstone 

 with all the calcareous matter leached out ; it is of a dark greenish grey, iron-stained 

 along the cracks and in the fossil-cavities. The original of Jaekel's fig. 6 is on a slab 

 12 cm. long and from 6 cm. to 10 cm. wide, which bears the imprints of Plectambonites 

 sericea, Leptaena alF. rhomhoidalis, Lingula sp., with fragments of a small Orthis 

 and 1 Rafinesquina siluriana. Comparison with the rock-descriptions and fossil-lists 

 published by Fearnsides, Elles, & Smith (1907) leads to the conclusion that the 

 specimens must have come either from the upper part of the beds which they call 

 Bardahessiagh beds, or from the lower part of the overlying Killey Bridge beds. There 

 is no sharp line of division between the beds, but those authors state (p. 102) with 

 regard to the latter division that " the lowest partly flaggy beds abound in innumerable 

 fragments of Lamellibranchs, Gastropods, Crinoids, and Cystids." The Bardahessiagh 

 and Killey Bridge beds are placed by the same writers in the Lower Ashgillian, and 

 correlated with the lower and upper parts of the Keisley Limestone of the Lake 

 District, and of the Sholeshook Limestone of S. Wales ; in the Girvan area their 

 respective equivalents are held to be the Quarrel Hill beds and the Trinucleus mud- 

 stones. The Tirnaskea beds, which succeed the Killey Bridge beds, are correlated with 

 the " Thraive beds of Girvan," by which presumably is meant the Drummuck Group, 

 comprising the Starfish bed. If these correlations are correct, then Pleurocystis anglica 

 is a little older than the Girvan species, and probably a little younger than P. Riigeri. 

 This is precisely the conclusion to which I had come from a study of the species itself, 

 before I had any external evidence as to its precise geological age. 



§ 468. Type-material. — Dr Jaekel (1899, p. 235) mentions two syntypes of this 

 species belonging to the Vetenskapsakademi, Stockholm. Through the kindness of 

 Prof. Gerhard Holm I have been able to examine these. One of them is the original 

 of Jaekel's fig. 6, the other of his fig. 6a, and they will be referred to here by those 

 numbers. 6 is the imprint of the antanal face of the lower part of a theca, with a long 

 stretch of stem (our PL V. fig. 60). 6a is the imprint of the anal face of the lower 

 part of another theca (our PI. V. fig. 62). The locality and mode of acquisition of 

 these two specimens was unknown to the Stockholm authorities, but they were believed 

 to be of British origin and to have been obtained at the same time. The close 

 similarity of the matrix confirms the view that both came from the same locality 

 and horizon. 



Fortunately 6a proves to be the counterpart of No. 25704 in the Museum of Practical 

 Geology, and that specimen is definitely labelled Bardahessiagh (PI. V. fig. 61). 



