Carboniferous Ostracoda from the Gay ton Boring. 249 



hundreds. The majority are single valves ; and all of them are 

 thick-shelled and have a robust appearance. 



In the hand-specimens referred to we found — in the greenish-grey 

 shale (at 731 feet), a few Ostracoda, and numerous fragments of 

 calcareous organisms, chiefly of Serpulce, some of Shells, and some 

 possibly Encrinital : — in the bluish-grey shale (at 730 feet), many 

 Ostracoda, besides numerous calcareous fragments as above. 



In both shales the organic remains are crowded here and there 

 along irregular planes and in other groups. 



For the lists of fossils in the associated beds see Quart. Journ. 

 Geol. Soc. Aug. 1884, pp. 487-8. 



Remarks on the Species. 



1. Kirkbya variabilis, sp. nov. PI. VII. Figs. 4a, 46 (type) ; 5a, 

 5b (var. a) ; 6, la, lb (var. 6) ; 8a, 86 (var. c). 



The prevailing form among this little group of Ostracods is a 

 Kirkbya which has strong Beyrichian affinities. Some specimens of 

 it are scarcely to be distinguished from such unisulcate species of 

 Beyrichia as B. arcuata (Bean) ; but most examples show the valves 

 ribbed after the fashion of Kirkbya, in which genus we place it. 



It varies much in relative length and height ; some specimens are 

 nearly twice as long as high, others are only a fourth longer than 

 high, while some, indeed, are nearly as high as long. What may 

 be taken as the local typical form, being the most common, can be 

 described thus : 



Suboblong in outline, height rather more than half the length, 

 dorsal border straight, ventral border convex, extremities rounded. 

 The more compressed end, which we take as the anterior, 1 is more 

 perfectly rounded than the posterior, which projects above, and is of 

 less height than the other. Valves compressed in front, swollen 

 behind, with a transverse subcentral sulcus ; this is crossed by a 

 strong longitudinal rib, which gives its lower portion the form of a 

 subcentral pit ; traces (more or less strong) of another and lower 

 rib are usually present along the ventral convexity of the valve ; 

 and there is nearly always a narrow, sharp-edged rib near to, and 

 almost parallel with, the dorsal margin. The valves are thick-shelled 

 and the right is larger than the left, and overlaps it strongly along 

 the ventral and extreme margins. Seen from above almost lanceolate 

 in outline, with the greatest diameter behind. Surface smooth. 

 Length -§V to -gV inch. 



Var. a. Figs. 5a, 56. 



This is a shorter form, being only a fourth longer than high ; with the 

 ventral margin more convex, and with the posterior extremity much 

 the highest. The sulcation and costal arrangement are the same, 

 and the right valve overlaps the other, as in the type form. 



Var. 6. Figs. 6, la, lb. 



This variety is short and high, like that just noticed, but the 



1 This is the view we take now ; but it was not followed throughout in a former 

 paper on Kirkbya, Ann. Mag. N. H. March, 1885. 



