194 DR. F. J. NORTH ON' [vol. lxxvi, 



the beak, which is small, pointed, slightly incurved, an<l situated 

 well above a line perpendicular to the plane of the brachial valve. 

 Width of the area at the hinge-line rather more than three times 

 its height, apical angle about 130° ; delthyrium narrow, its width 

 at the base being one-third of its height, delthyrial angle about 

 18°. Sinus shallow, with a median angular costa in the anterior 

 half, corresponding to the costa on the fold in the opposite valve. 

 The sinus is produced anteriorly into a quadrate tongue-like pro- 

 jection ; a line along the bottom of the sinus from the beak to the 

 anterior margin is evenly curved, and is practically a quarter of a 

 circle. 



Brachial valve convex, the greatest convexity being between 

 the middle line and the anterior margin ; mesial fold distinct, but 

 not much raised above the general level of the valve, except 

 towards the anterior margin. The mesial fold is divided by a 

 shallow median depression, increasing in width from the beak to 

 the margin of the valve, and on the floor of which in its anterior 

 half there is a pronounced subangular costa. 



Each lateral slope in both valves bears nineteen or twenty low 

 rounded costse, usually simple, but occasionally bifurcating and 

 decreasing gradually in size as they approach the cardinal ex- 

 tremities. 



Shell-structure unknown ; in none of the specimens examined 

 was the shell-substance sufficiently well-preserved to admit of 

 microscopic examination. 



Internally the delthyrial supporting-plates are perpendicular to 

 the plane of the cardinal area, and in cross- sections near to the 

 beak they appear as a pair of close parallel plates not connected by 

 a transverse plate. There is no median septum in the pedicle- 

 valve. 



Horizon and localities. — This species occurs in the Dibuno- 

 pJiyllum Zone, D 2 -D 3 , ' Brachiopod-Beds.' The locality of the 

 holotvpe is Beeston, near Waterhouses (Staffordshire) ; it is also 

 represented by smaller specimens at Park Hill and Castleton 

 (Derbyshire). 



The holotvpe is in the Museum of Practical Geology, Jermyn 

 Street, London, and is numbered 28422. 



IV. ' Spiriferina ' laminosa (M'Coy) : Ttlothyris, gen. nov. 



The species Sp. laminosa M'Coy has given rise to considerable 

 discussion. It has at various times been referred to at least four 

 genera', in addition to the one to which it is assigned in this paper, 

 and in it have been included forms which, although slightly 

 resembling it in external characters, really belong to other 

 genera. 



The uncertainty in the use of the name is to be attributed to 

 two circumstances: (1) M'Coy's original description is inadequate, 

 and his figures are too crude to portray clearly the characters of 

 the species, while the holotvpe, which was originally in the Griffith 



