8 



BRITISH FOSSILS. 



a glabella (the only part known) considerably wider, which miglifc 

 be due to pressure, has this portion tuberculate, as I found by ex- 

 amination of the original specimen, in 1845. 



History. — Very little has been contributed to the history of these! 

 species since Col. Portlock's account, for the simple reason that the 

 species are very rare in Britain, and have not yet occurred in other 

 countries ; and the author himself did not clearly make out either 

 the number of body rings or the structure of the tail, and he over- 

 looked the eyes. The genus was at once admitted in the classifi- 

 cation proposed by Dr. Emmrich in 1845, and placed at the end of 

 the Glenoid group ; but the number (12) of body rings proposed 

 there, although an improvement upon Col. Portlock's enumeration 

 (who included the neck segment and the first of the tail) was erro- 

 neous, and the distinction between it and Olenus very obscurely 

 defined, owing chiefly to the original mistake about the eyes. 

 M. Corda, too, in his general descriptions and figures of the Trilo- 

 bite genera, corrected the description of the eyes in Remopleurides 

 laterispinifer, which he, however, represented with thirteen body 

 rings and a bifurcate tail. A closely allied species from Bohemia is 

 there more correctly figured and described. The genus appears to 

 be entirely Lower Silurian. 



Explanation of Plate VIII. 



Fig. 1. Remopleurides Colbii. Col. Portlock's original specimen, Tyrone ; and the same 

 magnified, and dissected ; in fig. a, the left free cheek or wing is represented as- 

 separate, but it is not known whether the wings were connected in front — the 

 front portion of the head is restored in dotted lines ; at b, the 3d or 4th thorax 

 segment showing the prominent fulcra * * ; at c, the 7th segment, the broken 

 pleurae appearing not to have been produced into spines ; at c?, the last 

 segment ; e, the tail, its serrate edge restored from better specimens ; / show* 

 the striated external surface, and the groove and fulcrum of two of the pleurae. 

 Several portions of the crust are preserved in this specimen. 



Fig 2. Remopleurides laterispinifer. The original specimen ; an internal cast only ; at 

 2 b, the 7th and 8th thorax segment magnified ; at 2 c, the broken tail ; the 

 outline restored in dots. 



Fig. 3. Remopleurides dorsospinifer. Original specimen ; at 3 c, two of the thorax 

 segments in the front pleurae, internal cast, showing the grooves deeper than 

 in fig. 1 /; 3 c?, the 7th and 8tli segment of the axis, the latter with the long 

 dorsal spine. 



Fig. 3 a, 3 Two views of the head of another specimen, same locality ; also figured 

 by Portlock. 



Fig. 4. A young perfect specimen, Tramore, Waterford ; somewhat elongated by 

 cleavage ; 4 a, 8th and 9th thorax segments, external surface ; 4 6, internal 

 cast of the 8th, showing no enlargement ; 4 c, the perfect tail, magnified. 



