F. R. C. Reed—On the genus Trinucleus. (il 
sutures and compound eyes, we should naturally turn to its earliest 
representatives for traces of these structures. It is in the first group, 
comprising Z. Murchison, T. Gibbsi, and 7. Htheridger, that the 
division of the genal areas by an oblique ridge is found, and this 
ridge has the course of the true facial suture in members of the 
Opisthoparia, and may possibly be regarded as marking the line of 
fusion between the free and fixed cheeks. The less modified stage 
in which fusion has not taken place would then be found in the genus 
Ampyz. In neither case are traces of compound eyes present along 
this line. The similar position of the pseudo-antennary pit in this 
genus and in Zrinucleus supports this comparison. Some species of 
Ampyz (e.g. A. nudus) also have oblique nervures originating from 
the same place in the axial furrows as in Zrinucleus, and running 
obliquely back across the cheek to the point of section of the posterior 
margin by the facial suture, which suggests that they are structures 
similar to the radiating nervures in Z. Murchisoni, and to the 
posterior or outer part of the ocular ridge beyond the ocellus in 
the 7. seticornis group. 
In the Conocoryphide (Eastman-Zittel, 1913), in which compound 
eyes and ocelli are absent, but in which narrow free cheeks are found 
separated off by true oblique facial sutures, there are groups of 
nervures radiating out from the same place on the axial furrows 
as in Zrinucleus. This diffuse innervation of the genal areas is 
a conspicuous feature amongst blind trilobites, and is especially 
developed in Liocephalus! of the Conocoryphide and in Dionide. The 
loss of eyes is found to be correlated with the straightening of the 
facial sutures and reduction in width and size of the free cheeks in 
higher genera (e.g. some species of J//enus* and Trimerocephalus)® ; 
or the facial sutures may entirely disappear by coalescence of the free 
and fixed cheeks, as in Typhloniscus* and some species of Phacops.° 
2. Fringe. 
A difficulty meets us at this stage when we cease to regard the 
marginal suture on the edge of the fringe as representing the conjoint 
facial sutures as in Beecher’s theory, for the question of its 
correlation has to be faced. In answer to this we may suggest that 
it is possible that the lower plate of the fringe represents a reflexed 
anterior segment of the head-shield, and that the marginal suture is 
the divisional line between this and the first segment of the superior 
surface. The bending round ventrally of the anterior part of the 
crustacean head in its phylogenetic development is part of Bernard’s° 
annelidan theory of the origin of the Crustacea. Bernard held that — 
while the typical Crustacean head only consisted of five somites some 
of the trilobites possessed six somites in the cephalic shield. Early 
1 Grénwall, Bornholms Paradoxideslag (Danmarks geol. Undersog., ii, No. 13), 
1902, p. 102, t. 2, fig. 2. 
2 Reed, Q.J.G.S., vol. lii, pp. 414-16, pl. xx, figs. 1-3, 1896. 
3 Gurich, Verh. Kais. min. Ges. St. Petersb., ser. 11, Bd. xxxii, p. 359, 
+. xv, figs. 7a, b, 1896. 
4 Reed, GEou. MaGa., Dec. V, Vol. V, p. 433, pl. xiv, figs. 1-3, 1908. 
> Gurich, op. cit., p. 362, t. xv, figs. 4a, b. 
© Bernard, Q.J.G.S., vol. 1, p. 411, 1894. 
