Pahrozoic Bivalved Entomoslraca. 189 



We formerly looked upon this species as referable to the 

 genus Beyrichia ; but the general outline of the carapace, its 

 compressed sides, marginal ridges, reticulated surface, and 

 subcentral pit lead us now to place it, without much hesita- 

 tion, in Kirkbya, whilst its vertical ridges find an analogy in 

 the median ridges of the next species. 



It was discovered by Mr. John Young, of Glasgow, in the 

 Carboniferous-Limestone series (Upper) of Orchard, near 

 Thornliebank, Renfrewshire ; and it also occurs in the same 

 position at Kinneil Mill, Linlithgowshire. 



11. Kirkbya Urei, Jones. (PI. III. fig. 19.) 



Kirkbya Urei, Jones, 1859, Trans. Tyneside Field-Club, vol. iv. p. 136. 

 Kirkbya Urei, J. & K., 1867, Trans. Geol. Soc. Glasgow, vol. ii. p. 220; 



and 1871, vol. iii. Suppl. p. 29. 

 Kirkbya Urei, Jones & Holl, 18(39, Ann. & Mag. Nat. Hist. ser. 4, 



vol. iii. p. 225. 

 Kirkbya Urei, Jones, 1870, Monthly Microscop. Journ. vol. iv. p. 185, 



pi. lxi. f. 15 a, b. 

 Kirkbya Urei, Armstrong and others, 1876, Catal. W.-Scot. Foss. p. 45. 



Oblong, with ends rounded and nearly alike, and of equal 

 height to the rest of the valve, height equal to two thirds of 

 the length, strongly ribbed concentrically, thick-shelled. 

 Dorsal border straight and four fifths of the maximum length ; 

 ventral border straight or very slightly concave, and sloping 

 evenly up into the curvature of the extremities. There are 

 three strong concentric ridges on each valve ; the two outer- 

 most of which (speaking of the single valve) are marginal, and 

 follow more exactly the contour of the valve, while the third 

 forms, as it were, an escutcheon in the centre and is attached 

 to the second, or inner one of the two marginal dorsal 

 ridges ; within the escutcheon is usually a more delicate, 

 sharply bent ridge, U- or V-shaped, with the subcentral oval 

 pit at its base. The surface is strongly reticulated, the 

 meshes often being more or less rounded and irregular in size. 

 Edge view (lateral contour) compressed ovate or suboblong, 

 with the anterior end the narrower. Viewed from below, 

 little is seen of the carapace but the four ventral ridges with 

 intermediate reticulated spaces and the ridges of the escutcheon; 

 the view from above (fig. 19, b) shows a broad obtusely angu- 

 lated dorsal area, widest at the posterior end ; along this area 

 the two marginal ridges are continued (in less strength), single 

 rows of meshes separating them from each other. Length 

 -sV-^ inch. 



This is one of the smaller forms of the genus. Some spe- 

 cimens are relatively longer than others, and some have the 

 extreme dorsal and ventral regions well rounded, and so arc 



Ann. & May. N. Hist. Ser. 5. Vol. xv. 14 



