84 TRILOBITES OF GIRVAN. 



1852. Arethusina konincki, Barrande, Syst. Silur. Bolieme, vol. i, p. 495, pi. xviii, figs. 1 — 21. 



1808. Arethusina Jconincki, Barrande, Reapp. d. g. Arethusina, figs. 4 — 0. 



1884. Arethusina Jconincki, Tornquist, Undersokn. Siljans. Trilobitf., p. 51, pi. ii, figs. 10, 11. 



Specific, Characters. — Barrande's description of this species may be summarised 

 as follows : — 



General shape oval; head-shield occupying about one fourth and pygidium about 

 one twelfth of the whole length. 



Head-shield broadly semicircular, with narrow border separated off by mar- 

 ginal furrow and prolonged into genal spines parallel to axis and reaching 

 back to sixth pleurae. Posterior margin of head nearly straight. Occipital ring 

 prominent, with median tubercle. Neck segment behind cheeks widening laterally. 

 Axial furrows deep, almost parallel, uniting nearly at right angles in front of 

 glabella. Glabella short, subcylindrical or slightly conical, strongly convex; varying 

 somewhat in width in relation to cheeks. Three pairs of lateral furrows present on 

 glabella, but only posterior ones usually visible, marking off small ovoid basal lobes. 

 Fixed cheeks uniting in front of glabella in broad area. Free cheeks rather large, 

 subtriangular, with genal spines. Eyes prominent, rounded, situated opposite first 

 lateral furrows of glabella, and connected with it at this level by transverse eye- 

 lines. Fixed and free cheeks ornamented with minute pits irregularly distributed. 



Thorax of twenty-two segments ; axis convex, about half the width of lateral 

 lobes. Lateral lobes horizontal, bending down slightly in outer fourth. Pleurae 

 rectilinear, with strong diagonal furrow and rounded extremity. 



Pygidium transverse, forming segment of circle, three 'times as wide as long, 

 surrounded by narrow border. Axis prominent, about one fifth the whole width 

 of the pygidium, and showing six segments. Lateral lobes almost horizontal, with 

 4—5 pleurae, each with diagonal furrow. 



Remark*. — A single minute head-shield in a fair state of preservation and several 

 pygidia in Mrs. Gray's collection from Balclatchie afford the only evidence for the 

 occurrence of this Bohemian and Swedish species in the Girvan area. But it seems 

 impossible to do otherwise than refer these specimens without much doubt to 

 Barrande's species, Arethusina JconincM, after a careful comparison with a large 

 number of Bohemian examples. 



In the Girvan specimen of the head-shield all the typical features are seen. 

 The course of the facial sutures and the eye-lines are distinct, but the latter are 

 rather oblique instead of horizontal, though this may be due to the distortion 

 which the specimen has evidently suffered through crushing. The punctation of 

 the cheeks, the narrow border, the genal spines and the short glabella are well 

 seen ; the basal lobes are indistinct owing to the surface of the glabella being 

 injured. The pygidium appears to offer no points of difference. 



The genus Arethusina has been recorded by Walcott 1 from the Prospect Mountain 

 1 Walcott, " Palseont. Eureka district," ' Mon. U.S. G-eol. Surv..' vol. viii (1884), p. 02. pi. 9. fi»-. 27. 



