46 CARBONIFEROUS LAMELLIBRANCHIATA. 



Kensington, and a new drawing of it is given in the accompanying PI. VII, fig. 2. 

 Phillips says that " it may possibly be Avicula," but de Koninck was the first 

 observer who recognised the distinctive characters of the shell and separated it 

 under his new genus Rutotia. Unfortunately, shells belonging to the genus had 

 been recognised and described previously from Permian beds under the name of 

 Eumicrotis, and this must therefore have precedence. 



The type specimen is a left valve, which shows the ear-like process in front and 

 the absence of any posterior ear. I have fortunately been able to obtain some right 

 valves, which show a fairly well -formed though small anterior ear, separated from 

 the rest of the valve by a deep and broad notch for the byssus. PI. VII, fig. 1, 

 represents a bivalved example with the right anterior ear wanting, from the Carbo- 

 niferous Limestone of Hill or El Bolton, Craven district of Yorkshire. PI. VII, 

 fig. 4, shows the right valve, with the anterior ear well preserved. 



E. hemisphxricus is very like the shell I figured as Posicloniella gibbosa in Vol. I, 

 PI. V, figs. 12 — 14. I should not feel it an easy task to determine the left 

 valves, but fig. 12 shows both valves to have been equally gibbose, and the right 

 valve seems to have had no ear. 



Eumioeotis ovalis, de Koninck, sp., 1885. Plate XI, figs. 8, 9; Plate XVIII, figs. 8, 9. 



Eutotia ovalis, de Koninck, 1885. Ann. Mus. Roy. d'Hist. Nat. Belg., torn, xi, 



p. 200, pi. xxii, figs. 36, 40. 

 ornithocephala, de Koninclc, 1885. Ibid., p. 200, pi. vii, figs. 29, 30 ; 

 pi. xxii, figs. 25, 29. 



Specific Characters. — Shell below medium size, slightly inequivalve, slightly 

 obliquely ovate, gibbose. Its margins rounded. The hinge-line straight, not 

 extending very far backwards. The umbones comparatively large, gibbose, 

 pointed, incurved, twisted slightly forwards; the left only slightly more gibbose 

 than the right, subcentral, separated by an area. The anterior ear well formed in 

 the right valve and separated by a byssal slit from the rest of the valve, not so well 

 marked in the left valve. The posterior ears obsolete, the posterior superior edge 

 of the valve being small ; the angle very obtuse. 



Interior. — Unknown. 



Exterior. — The surface is smooth, even concentric lines of growth being hardly 

 visible. 



Dimensions.— -PL XVIII, figs. 8 and 9, a bivalved example from Settle, measures — 

 Antero-posteriorly .... 24 mm. 



Dorso-ventrally . . . .25 mm. 



From side to side . . . .14 mm. 



