120 BRITISH CAMBRIAN TRILOBITES. 



much depends upon the state of preservation. Indeed, Salter, whose figures 

 show only four, says that there are six, which is the number represented by 

 Angelin. The principal difference lies in the outline, the lateral borders in 

 D. furca being straighter and making a more definite angle with the anterior 

 border than in D. dicraeura: but it should be remembered that our specimens are 

 distorted and the Scandinavian ones are incomplete. 



The head shown in Plate XIV, fig. 11, is similar in character to that doubtfully 

 ascribed by Salter to this species. It corresponds very well with the tails in size, 

 and it comes from the same locality and horizon as that represented in fig. 13, 

 about which there can be no question ; but the chief reason for referring it to this 

 species is the resemblance of the glabellar furrows to those of D. dicrseura, as 

 figured by Moberg and Segerberg. It differs from this form in the presence of a 

 distinct ridge defining the inner edge of the wide margin. There can, however, 

 be little doubt that this ridge has been greatly accentuated by compression, and 

 in the original condition it was probably much less conspicuous. In D. villebruni, 

 Bergeron, 1 which seems to be closely allied, the outer half of the broad margin is 

 concave and the inner half convex ; and if such a margin were crushed against 

 the cheeks and glabella, the convex portion would naturally be compressed into a 

 ridge. 



All of Salter's figures are from specimens belonging to Mr. Ash and coming 

 from Moel-y-gest. Mr. Ash's collection seems to have been dispersed ; but in 

 the Sedgwick Museum there is a specimen of D. furca lettered a. 30 (see Plate XIV, 

 fig. 12), and in Salter's Catalogue 2 Mr. Ash is stated to be the donor and the 

 locality is given as Moel-y-gest. Probably this is the original of Salter's plate 

 viii, fig. 10, or else its counterpart. 



Horizon and Localities. — Upper Tremadoc : Moel-y-gest and Garth Hill, 

 Portmadoc. 



Genus APATOKEPHALUS, Brogger. 



The name Apatokephalus was proposed by Brogger. who looked upon it as 

 denoting a subgenus of Dilcelocephalus. The type species is the Trilobites serratus 

 of Boeck, which was originally founded upon the tail alone ; but Holm has shown 

 that the cranidium subsequently described by Linnarsson as Bemopl 'en rides dubius 

 belongs to the same species. Since this cranidium is so very different from that of 

 Dilcelocephalus it seems better to look upon Apatokephalus as a distinct genus. 



The glabella is urceolate, the posterior portion, exclusive of the neck-segment, 

 being greatly expanded, the anterior portion narrower, tongue-like. The eyes 

 are long, crescentic, and almost touch the glabella at their extremities. The 



1 Bull. Soc. Geol. France, [3] vol. xxiii (1895), pi. v, figs. 1, 2. 



2 Cat. Camb. Sil. Foss. Mus. Cambridge, p. 17. 



