118 F. R. C. Reed—On the genus Trinucleus. 
V.—Sepewicx Museum Nores. 
Nores on tHE GENUS Z'RrINUCLEUS. Part LY. 
By F. R. Cowper REED, Sc.D., F.G.S. 
Tur Gunat AREAS. 
(J\HE triangular non-perforated areas lying on each side of the 
glabella and bounded in front and laterally by the fringe are 
usually described as the cheeks and distinct from the fringe, as if they 
alone corresponded to the fixed cheeks of the Opisthoparia and 
Proparia, or even included also the free cheeks of these orders. 
But if the facial suture is marginal, and if the lower plate of the 
fringe is considered to represent the free-cheeks, as Beecher’ 
maintained, the upper plate of the fringe must be regarded as 
merely a modified marginal portion of the fixed cheeks, so that the 
triangular areas within the fringe would only constitute the inner 
part of the fixed cheeks. 
Whether we regard this view of the homologies of these structures 
as correct or not (see below), we must note that there is sometimes no 
sharp demarcation of the fringe from the so-called cheeks, scattered 
pits (particularly near the genal angles) occurring within the 
generally regular inner limits of the fringe, as for instance in 
T. concentricus of the Onny River (Guot. Mae., Dec. V, Vol. IX, 
p. 349, Pl. XVIII, Fig. 4, 1912). 
It is, however, convenient to describe these so-called cheeks apart 
from the fringe, the characters of which have been discussed on 
a previous occasion (op. cit.), and we may accordingly term them 
the genal areas to avoid confusion and premature conclusions. 
There are three more or less distinct types of genal areas 
recognizable amongst the species of Zrinucleus, 1.e. : 
1. Genal areas divided into two more or less unequal portions by 
an oblique ridge or line of bending, each portion having 
a different surface ornamentation, ro a Murchisont, 
T. Gibbsi, T. Htheridger. 
2. Genal areas marked with a horizontal or slightly oblique line 
(‘‘ocular ridge” or ‘‘line’’) running outwards from: the 
side of the glabella to a median or submedian tubercle 
(‘‘eye’”’ or ‘‘ocular tubercle’’) and sometimes beyond it. 
The ornamentation of the surface is uniform. E.g. 7. setv- 
cornis, T. Bucklandt. 
3. Genal areas without any ridge or line, uniformly convex, without 
‘‘ocular tubercle”. ‘The ornamentation of the surface is 
uniform. E.g. 7. concentricus. 
These three types may now be described in detail, and their 
development and relations studied in various species. 
1. In Z. Murchisoni, Salter (see Grou. Mac., Dec. VI, Vol. I, 
p. 352, Pl. XXVIII, Figs. 4, 4a, 1914), a narrow semilunar area 
stretches along the inside of the fringe from the pseudo-antennary 
pits at the front end of the glabella to “the postero-lateral outer angle 
of the genal area, and is marked off from the rest of the genal area 
1 Beecher, Amer. Journ. Sci., ser. IV, vol. iii, pp. 100, 103, 183, 186, 1897. 
