40 TRTLOBITES OF GIRVAN. 



Remarks. — This form is exceedingly common at Dow Hill and Ardmillan, and 

 is represented by a very large series of specimens in Mrs. Gray's collection. 

 Nicholson and Etheridge figured some specimens of it as B. laterispinifer, Portlock, but 

 the examination of tAvo or three score examples, some of which are nearly perfect 

 individuals, have convinced me that it does not belong to this species, but may be 

 considered a variety of B. salteri. 1 In the head-shields the following characters of 

 B. salteri are noticeable: — (1) tuberculation of the basal angles of the glabella; 

 (2) tuberculation of the neck ring ; (3) two pairs of curved furrows on the glabella ; 

 and (4) faint granulation of the surface of the glabella. In the smaller specimens 

 from Grirvan the relative width of the anterior tongue of the glabella agrees pre- 

 cisely with that of the type examples from Waterford, but in the larger specimens 

 from Grrvan the tongue is relatively wider and more strongly bent downwards. 

 Probably this difference is only due to age. 



In several specimens from Girvan head-shields possessing the above characters 

 are found attached to thoraces which when isolated have been ascribed to B. lateri- 

 spinifer owing to the conspicuous enlargement of the seventh pair of pleura?. The 

 two specimens figured by Nicholson and Etheridge from Ardmillan and Ardwell as 

 belonging to the latter species (M., pi. x, fig. 11 ; pi. xi, fig. 15) should apparently 

 be assigned to this variety of B. salteri; the glabella of fig. 15 does not show the 

 characteristic two pairs of furrows, but the shell is preserved in this case, and it is 

 only in casts that the furrows are distinct. The ornamentation of these figured 

 specimens does not agree with that given by Salter 2 for B. laterispinifer. 



In the specimens from Dow Hill the axial rings show a single row of large 

 granules on their anterior half, with sometimes a less regular row behind ; a faint 

 transverse line is sometimes seen dividing each ring into an anterior and a posterior 

 portion. The posterior portion is furnished with short triangular marginal 

 spines, coarser near the sides and giving a serrated aspect to the edge. The 

 axis is gently convex, and more than twice as wide as the pleura?, tapering 

 posteriorly at an angle of about 30°. The pleura? are short and falcate, with the 

 characteristic prominent fulcral tubercle, short oblique furrow, and free recurved 

 point. The upper surface of the pleura? shows a few longitudinal striations on the 

 anterior portion, but the under surface is crossed by regular transverse equidistant 

 striae. The seventh pleura? are slightly stouter than the others, and are produced 

 backwards into long, straight, tapering spines reaching to the end of the pygidium. 

 The eighth axial ring has a strong median tubercle which may represent the base 

 of a spine broken off short. 



The pygidium is transverse, wider than long, subquadrate, with the posterior 

 margin serrated by the four short angular points of the two pairs of pleura?. The 

 lateral lobes consist of these two pairs of pleura?, which are short and curved back 



1 Seed, ' Quart. Journ. Cleol. Soc.,' vol. lv (1899), p. 747, pi. xlix, figs. 1—3. 

 Salter, ' Mem. Geol. Surv.,' dec. vii (1853), pi. viii, fig. 2. 



