822 DR. F. R. C. REED ON THE 



known. The " upper " valve shows no foramen and no internal characters which would 

 lead us to place it with the Discinidw : there is no trace of a pedicle-tube or groove. 

 "The shape of the shell, the incurved pointed apex, and its general aspect suggest that 

 it should be referred to the gasteropod genus Archinacella or to some allied patelliform 

 genus. Probably Portlock's specimens from Desertcreat should also have the same 

 reference. We may remark that it bears a considerable resemblance to Archinacella 

 orbiculata (Hall),* A. deleta (Sardeson),t and allied species from the Ordovician of 

 America. 



Genus Philhedra, Koken. 



Philhedra drummuckensis, sp. nov. 



(Plate IV, figs. 26-29.) 



Shell circular. Upper valve conical, capuliform, with pointed apex situated 

 excentrally at about one-fourth to one-fifth the diameter of valve from posterior 

 end, with steeper posterior slope. Surface of valve covered with closely set fine 

 radiating lines of minute radially elongated pustules, and a few irregular concentric 

 growth-ridges. 



Dimensions. — Diameter, 5-5 "5 mm. ; height, 2-2 '5 mm. 



Horizon. — Drummuck Group (Starfish Bed). 



Locality. — Thraive Glen. 



Remarks. — The general affinities of this shell seem to be with Ph. rivulosa 

 (Kutorga)4 but it is much more closely allied to the species Ph. mullochensis 

 described below, though it has a more pointed apex. The internal characters are 

 not satisfactorily preserved. 



Philhedra mullochensis, sp. nov. 

 (Plate IV, figs. 30-33.) 



1883. Crania siluriana, Davidson (pars), Man. Brit. Foss. Brach., vol. v, Silur. Suppl., p. 215, pi. xvii, 

 figs. 51-53 (non figs. 49, 50). 

 Non 1866. Crania siluriana, Davidson, op. cit., vol. iii, pt. vii, p. 82, pi. viii, figs. 19, 20. 



Shell subcircular. Upper valve convex, capuliform, rounded, subcorneal, with 

 blunt apex situated near posterior margin at about one-fourth to one-third the 

 diameter of the shell. Surface of valve covered with minute pustules arranged in 

 very numerous closely placed regular radial rows ; one or two coarse irregular low 

 rounded concentric rugse usually present. Interior of upper valve with pair of 

 faintly impressed large anterior occlusors, and slightly thickened internal margin. 



Dimensions. — Diameter, 9-11 mm. ; height, 3-4 mm. 



Horizons. — (l) Mulloch Hill Group ; (2) Saugh Hill Group. 



Localities. — (l) Mulloch Hill, Craigens ; (2) Newlands. 



* Ruedemann, Bull. 525, New York Educ. Dep. (Mus. Bull. 162), 1912, p. 108, pi. 7, figs. 1-6. 



f Ui.uich and Soofield, Palseont. Minnesota, vol. iii, pt. ii, 1897, p. 831, pi. lxi, figs. 16-20. 



{. Von Huene, Verhundl. Euss. Miner. Gesellsch. St Petersburg, ser. 2, vol. xxxvi (1899), p. 300, t. iv (xii), figs. 8-16. 



