BRITISH FOSSILS: 



5 



so much outwards as in our figure) as far as the origin of the tail. 

 In all other respects the body rings agree with those of the R: 

 Colbii. 



The tail is broken, and has lost all but the anterior margin and 

 the axis ; the latter is of two rings, and their shape is as in the last 

 species. Immediately beneath the axis there is an emargination like 

 that represented in Portlock's figure ; but it is, I believe, a fold of 

 the incurved under portion, and is certainly not a part of the margin 

 of the tail, which indeed, from the proportions of the fi:agment left, 

 would have been of just the shape of that of R. Colbii. 



British Locality and Geological' Position. — Lower Silurian. 

 Townland of Bardaliessiagh, Tyrone, in micaceous sandy schist. 



EEMOPLEUEIDES DORSOPINIFER. . 

 Figs. 3, 4. 



Diagnosis. R. elongatus longiovatus, glabelld madcimd quam lata longiori, 

 ad frontem inter oculos angustd ; genis parvis, in spinas breves extensis ; 

 thoracis axi latissimo, antice pleuram ter superante, segmento octavo in- 

 crassatOy in spinam for tern extenso ; pleuris brevibus, fiilcro ut in prcBcedenti ; 

 caudcE margini quadrispinoso, spinis externis brevioribus. 



Synonyms* R. dorsopinifer, Portlock (1843), 1. c, pi. 1. fig. 3. also fig. 4. 

 M'COY (1846),. SjD. Carb. Foss. Irel. 43. 



Description. — Length one inch. The general shape is more elon- 

 gated than in the two foregoing species, and the anterior produced 

 portion of the glabella is scarcely more than one third its entire 

 width ; otherwise the proportions of the head and its parts are very 

 similar. The body rings, except in the narrower axis, agree in 

 structure with those of -R. Colbii, and R. laterispinifer ; the rings of 

 the axis have their posterior edge serrated, and their surface granu- 

 lose ; and the pleurse are similar in shape, and in the position of the 

 fulcrum. The chief difference is in the comparative width of the 

 axis, which is not three times the width of the pleurae in front, and 

 posteriorly is not so much narrowed, being little less than half 

 the width it has in the anterior part. The seventh pair of pleurae, 

 too, are not at all elongated, at least not in the young and perfect 

 specimen, fig. 4 (in fig. 3, Portlock's original specimen, this portion 

 is broken ofi"). The eighth segment of the axis is incrassated, and 

 gives birth to a short spine which extends backward, lying closely 

 on the segments, nearly to the end of the tail ; the tip of the spine 

 hi a little recurved, and its surface striated. The incrassation of the 

 [vii. viii.J 7 H 3 



