4 



BRITISH FOSSILS, 



There is one genus, liowever, to which, though perhaps not identi- 

 cal, our fossil has a very great similarity, we mean Tiresias, described 

 by Professor M^Coy, from the head only. The species T. insculptus, 

 found also in the Chair of Kildare, differs from ours by its greater 

 size, the glabella p3n:iform instead of half-egg-shaped, and marked on 

 the sides by two pair of glabella furrows ; the posterior angles of the 

 head too are prolonged. But in the general form, lineation of the 

 cheeks, &c., the two are very much alike, and when more specimens 

 are found, it is quite possible that Cyphoniscus may be found to be 

 a sub-genus only of Tiresias, distinguished by its lobeless glabella 

 and blunt not produced head angles. That genus, like ours, cer- 

 tainly had a minute maxillary portion or free cheek, and judging 

 from the description, the eyes appear to have been also linear and 

 very forward. 



British Localities and Geological Position. — Llandeilo Flags ; 

 Limestone of the Chair of Kildare, county of Kildare, Ireland. 



Explanation of Plate IX. 



Fig. 1. Small specimen, partly coiled. 



Fig. 2. Young individual, with tall and seven thorax joints. In this specimen there is 

 a portion of an eighth segment above the others, but this is probably part of 

 the neck segment. 



Fig. 2*. The same, magnified, the axis of the tail not very large. 



Fig. 3. Young imperfect speeimen, seven body rings. 



Fig. 3*. Do., magnified. 



Fig. 4. Full grown head. 



Fig. 5. Full grown tail of a variety with larger axis than usuaL 

 Fig. 5*. The same, magnified. 



Fig. 6. Magnified figure of the head, two thorax rings, an anterior and posterior one^ 

 and tail. At a, the neck furrow curves upward, and terminates against the 

 outer margin ; 6, is the restored free cheek (lost i^^, all our specimens) ; c, the 

 position of the eye indicated ; d, the side part of the axis of the thorax rings, 

 running out into the pleural groove. 



Fig. 7. Lateral view of the head and three first thorax rings ; the free cheek and eye 

 are indicated as in the last figure. 



August, 1853. 



J. W. Salter. 



