178 
8EI.ACHIT. 
Type. Detached largo dental plates. 
Tho type species, of comparatively large size, the antoro-postenor 
measurement of the “ upper” dental plates being sometimes as great 
as 0'05, and the distance from the outer to the inner border 0'035. 
Outer margin of “upper” dental plate straight, inner margin 
nearly straight for its greater extent anteriorly and sharply curved 
upwards behind ; coronal contour slight!}' raised along a line con- 
necting tho bend of the inner border with tho posterior extremity of 
the outer border, and the abraded hollows in worn teeth apparently 
confined to the area in advance of this elevation. “ Lower ” dental 
plate gently and more uniformly rounded than the “ upper; ” inner 
border curved throughout its length. 
The “ upper ” dental plate is described as “ posterior ” by 
M‘Coy, and is figured by Davis {loo. cit. pi. Iv. figs. 1, 13, Id) and 
Traquair (Joe. cit. pi. xvi. fig. 4); tho “lower” dental plate is 
described as “middle” by M‘Coy, and is figured by Davis (loc. cit. 
pi. Iv. figs. 2, 10) and Traquair {loc. cit. pi. xvi. fig. 3). 
The finest example of the dentition yet known is that from the 
Cement Limestone of East Kilbride, Lanarkshire, described by 
Coutts and Traquair. According to the latter it exhibits, in 
addition to the ordinary largo dental plates, teeth identifiable with 
Ilelodus planus., II. rudis, II. Icevissimus, and II. didymus. 
Form. ^ Loc. Lower Carboniferous Limestone : Armagh, Ire- 
land ; Lanarkshire, Scotland ; Northumberland and Somersetshire, 
England. Carboniferous Limestone (various horizons) : Ayrshire, 
Scotland; Westmoreland and Derbyshire, England; Denbighshire 
and Flintshire, N. Wales. 
(i.) Armagh, Ireland. 
Unless otherwise stated, the following specimens are from the 
Enniskillen Collection : — 
P. 2394, P. 2406. Three “ upper ” dental plates, figured by J. W. 
Davis, loc. cit. pi. Iv. figs. 1, 13, 14. As already remarked 
by Traquair (loc. cit. p. 400) the inner margin of the first 
is erroneously placed externally ; the coronal surface of 
the second is much excavated by wear, and the postero- 
lateral and inner margins are abraded and broken. 
P. 2409. Twenty-five “upper” dental plates, of large size, some 
much worn, and others showing marks of incomplete 
division into teeth. 
P. 2409 a. Five large dental plates of irregular shape. 
