36 TRILOBITES OF GIRVAN. 



3. Remopleurides colbii, Port-lock, 1843. Plate V, figs. 17, a, b. 



1843. Remopleurides colbii, Fortlock, Geol. Rep. Londond., p. 256, pi. i, fig. 1. 



1845. Remopleurides kolbii, Emmricli, Neues Jahrb. f. Miner., etc., p. 45. 



1846. Remopleurides colbii, M'Coy, Synops. Silur. Foss. Ireland, p. 43. 

 1854. Remopleurides colbii, Morris, Cat. Brit. Foss., 2nd ed., p. 115. 



1863. Remopleurides colbii, Salter, Mern. G-eol. Surv., dec. vii, pi. viii, p. 1, figs. 1 a — -/. 



1865. Remopleurides colbii, Salter and Woodward, Chart Foss. Crust., fig. 40. 



1877. Remopleurides colbii, Woodward, Cat. Brit. Foss. Crust., p. 57. 



1879. Remopleurides colbii?, Nicholson and Etheridge, Mon. Silur. Foss. Girvan, fasc. ii, p. 146, 



pi. x, figs. 8, 8a. 

 1899. Remopleurides colbii, e. p., Mem. Geol. Surv., Silur. Bocks Brit., vol. i, Scotland, p. 674. 



Remarks. — The difficulty of distinguishing the species of Remopleurides by 

 isolated heads, particularly when in the state of casts, was experienced by Salter 

 and Nicholson and Etheridge. The original types of this species were poor, and 

 even the material which Salter used left much to be desired. This is especially 

 the case in the head of B. colbii, a species to which some specimens from 

 Drummuck were referred by Nicholson and Etheridge. One of their figured 

 specimens deserves a fuller description than they gave it, particularly because of 

 its well-preserved eyes. 



In this head-shield the glabella is convex from side to side and from back to 

 front, and seems to be not quite so regularly elliptical as Salter's figures of B. colbii 

 indicate, being somewhat wider at the base than elsewhere ; but it is slightly 

 distorted by oblique crushing and is only a cast. Apart from the tongue the 

 glabella is broader than long. There are obscure traces of two pairs of oblique 

 grooves on the surface, but I believe these are not true lateral furrows, but only 

 superficial injuries, which their somewhat irregular position and variable depth 

 suggest. The tongue is more than one third the length of the whole glabella, 

 and is rather more than half as wide ; it scarcely at all decreases in width 

 anteriorly, is very strongly bent down, and is truncate at its anterior end. A 

 furrow, interrupted in the middle, marks off a narrow anterior band on the tongue. 

 The eye-lobe is a very narrow band running along the side of the glabella right 

 up to the anterior end of the tongue. The eyes are vertical, semi-annular, and 

 indent the base of the glabella to rather less than one third its basal width, as in 

 //. colbii, but they increase in width anteriorly and at their front end are as wide 

 as the tongue is long, against which they rest — a feature not shown in Salter's 

 figure of B. colbii. The lens-bearing surface of the eye is nearly vertical ; the lenses 

 are arranged in regular, closely set vertical and diagonal rows. The vertical rows 

 near the base (not well preserved) contain about thirty lenses, and those near the 



