153 



Barrande and Burmeister. According to their definitions, a 

 very simple and natural group of Trilobites are retained to- 

 gether, two of the essential points being the division of the 

 glabella by three to four short furrows on each side, and the en- 

 tire margin to the pygidium. In 18f>3 Professor James Hall 

 re-defined Conocephalites* much enlarged it, and introduced 

 a number of species differing greatly from the European types. 

 In some of these the glabella is quite undivided, in others 

 there are two furrows on each side, whilst again the border of 

 the tail is produced in some into a spine on each side as in 

 Dikelocephalus, besides other modifications of structure. 



It would be more appropriate, I think, to retain such forms 

 separate from Conocephalites, as represented by the European 

 types of the genus G. Sulzeri and G. striatus. Indeed, Pro- 

 fessor Hall admits a difliculty in referring all his species to 

 Gonocephalites ; perhaps the difficulty might be solved by the 

 institution of a new genus for their reception. 



A well marked, and not often dwelt-upon character in 

 Go7iocephalites, is the presence of the ocular ridge or eye line. 

 This appears to be present more commonly in those species in 

 which the eyes are placed wide apart, as in G. striatus, Emmrich. 

 Burmeister describes it in the last-named species thus, "A 

 sharp ridge extends itself towards them " {i.e., the eyes), 

 " from the angles of the glabella."t This ridge is well dis- 

 played in some of the American Trilobites referred by Profes- 

 sor Hall to Gonocephalites, for instance, G. Eos, G. diadematus, 

 etc. Accepting Barrande's definition of the genus as the 

 correct and most satisfactory one, we have a cephalic shield 

 from the Mersey deposit, which appears to correspond 

 generally with it, although not absolutely identical. 



CONOCEPHALITES ? STEPHENSI (sp. nov.), 

 (Figs. 1—3.) 



Sp. char. — Cephalic shield, broad, semicircular, with a pro- 

 minent anterior, and rather flattened margin, glabella elongate, 

 enlarging somewhat towards the front ; neck segment, broad, 

 and well marked,without a tubercle. Glabella furrows, four in 

 number on each side, short, and becoming more pit- like towards 

 the front ; the basal pair are rather obliquely directed, and are 

 the longest ; the most anterior pair are situated in the angle 

 formed by the glabella, ft'ont margins, and fixed cheeks ; a 

 fifth short, and faint depression exists exactly in the centre of 

 the anterior margin of the glabella. The neck furrow is very 

 deep (in casts), and pit- like at the sides, at the junction of 

 the axal furrows. The latter are deeply excavated, but the 

 marginal furrow in front the glabella is faint. Fixed cheeks 

 broad, of a much less convexity than the glabella, and sub- 



* 16th Annual Report, State Cabinet, N. York, 1863, p. 147. 

 t Organisation of Tillobites, p. 73. 



