800 DR F. R. C. REED ON THE 



as the internal characters, distinguish this species from 0. audaoc. We may dedicate 

 this species to the Scotch geologist John Macculloch. 



Genus Paterula, Barrande. 

 Paterula balclatchiensis, Davidson. 



(Plate I, figs. 14-20.) 



1883. DiscAna ? balchtchiensis, Davidson, Mon. Brit. Foss. Brack., vol. v, Silur. Suppl., p. 210, 



pi. xvii, fig. 41 (non fig. 42). 



1884. Paterula balchtchiensis, Davidson, ibid., p. 391. 



Davidson's description of the species is sufficient except on one point ; for in the 

 types as well as in several other specimens of the pedicle-valve from Balclatchie 

 there is seen to be present the small narrow marginal slit or notch in the posterior 

 border which occurs in P. bohemica, Barrande, # representing the pedicle-passage. 

 Traces of a few very fine radial ridges are also visible on the interior in a few cases. 

 Hall and Clarke t hesitated in placing P. balclatchiensis in the genus Paterula 

 owing to the supposed absence of these characters. Certain specimens from the 

 shore at Bennane Head also show the pedicle-notch. Davidson recorded the species 

 from Drummuck as well as from Balclatchie, but the specimens possess certain 

 characters which warrant their separation, though he said they were " exactly 

 similar." The interior of one pedicle-valve from Dow Hill (fig. 18), probably referable 

 to P. balclatchiensis, shows a rhomboidal muscle-scar bluntly pointed anteriorly and 

 apparently composed of five (?) elements which cause the anterior edge of the scar to 

 be lobed and diverge in a fan-like* manner from the apex of the shell, reaching nearly 

 half its length. Hall and Clarke (op. cit., pi. ivK, fig. l) figure a somewhat similar 

 scar in a specimen attributed to Paterula (?) from the Quebec Group. The Ballantrae 

 specimens are poor, but seem indistinguishable from those from Balclatchie. 



Horizons. — (l) Balclatchie Group; (2) Ballantrae Group (Arenig). 



Localities. — (l) Balclatchie, Dow Hill ; (2) Shore at Bennane Head. 



Paterula ? aibida, sp. nov. 



(Plate I, figs. 21-25.) 



Shell circular or subcircular in outline, compressed. Pedicle-valve gently convex, 

 most so posteriorly, with submarginal slightly elevated small beak. Margin of shell 

 thickened regularly all round and forming smooth raised narrow band, specially 

 thickened along posterior edge, with minute triangular pedicle-groove across it 

 behind beak ; rest of surface of shell ornamented with fine concentric striae. 

 Interior of shell with 3-4 very faint delicate lines radiating forwards from beak 



* Barrande, Syst. Silur. Boherne, vol. v, p. 110, pi. 95, fig. i, 1-3 ; pi. 152, fig i, 1-9. 

 t Hall and Clarke, Palmont. New York, vol. viii, 1892, Brach., i, p. 79. 



