416 ME. F. E. C0WPEE EEED ON THE [A-Ug. 1 896, 



head-shields in the Woodwardian Museum, Cambridge, collected by 

 Messrs. Marr and Nicholson and by myself. 



Affinities. — From 1". conifrons, Billings, our species is distin- 

 guished by the absence of eyes, the shortness of the axal furrows, 

 the non-gibbosity and shortness of the glabella, etc. The amount of 

 inflation of the head in the two forms is very similar and gives them 

 a spurious look of affinity. Our Keisley form belongs, however, to 

 that group of blind Illceni which have been described from Bohemia, 

 Russia, and Sweden ; I. Angelini (Holm) l and /. leptopleura (Linrs.) 

 are the two blind species known from Sweden. With the former 

 our British species agrees in the relative length and width of the 

 glabella and the fixed cheeks, in the course of the axal furrows and 

 of the facial suture, and in the absence of eyes ; but differs in the 

 amount of inflation and length of the head-shield. 1. ccecus (Holm) 2 

 from the ' Lyckholmer Schicht F ' 3 of the Baltic area comes very 

 close to our species except in the amount of inflation, breadth, and 

 curvature of the head-shield. The three Bohemian species, I. Katz- 

 eri (Barr.), /. Zeidleri (Barr.), and /. aratus (Barr.), bear comparison; 

 and all the seven appear to be closely allied by structural peculiarities. 

 But the absence of eyes, which leads to a modification in the course 

 of the facial suture and shape of the free cheeks, is said not to 

 be accompanied by any changes in other parts of the body ; and 

 Barrande and Holm do not consider that there is sufficient justi- 

 fication for the creation of a new genus, particularly as a similar 

 disappearance of the eyes and modification of the facial sutures and 

 free cheeks is found in the genus Conocephalites. 



IlL2ENUS, sp. (PI. XX. fig. 6.) 



One epistome of an lllcenus in the Woodwardian Museum 

 resembles somewhat closely that of 2". Davisi (Salter), but it is 

 longer and more pointed posteriorly. In shape this Keisley epistome 

 is broadly triangular ; its anterior side is gently arched forward, and 

 its posterior sides converge backward with a slight concave-outward 

 curve to meet at the rounded obtuse apex at an angle of about 135°. 



All the three sides are slightly bevelled, but otherwise the 

 epistome has a flat surface. Nine or ten strongly-marked furrows, 

 with raised ridges between them, run across the surface from side to 

 side. Those nearest the front border run across continuously almost 

 in a straight line from one lateral angle to the other; the more 

 posterior furrows bend backward in the middle with an increasingly 

 sharp and strong curvature as they are followed backward. Between 

 these strongly-bent posterior furrows and those in front are a few 

 short furrows and ridges in the middle of the epistome. The 

 anterior edge of the epistome is furnished with a broad smooth 



1 Holm, ' Svenska Arterna af Trilobitslagtet Wanus] Bih. k. sv. Yet.-Akad. 

 Handl. vol. vii. (1882) no. 3, p. 120, pi. iv. fig. 29. 



2 Holm, ' Ostbalt. liken.' Mem. Acad. Imp. Sci. St. Petersbourg, ser. vii. 

 vol. xxxiii. (1886) no. 8, p. 162, pi. xi. fig. 11 a-d. 



3 Barrande, ' Syst. Sil. Boheme,' pt. i. suppl. 



