EDMONDIA EXPANSA. 323 



and rugae, which become larger and further apart towards the lower margin. The 

 folds commence close together in the anterior part of the upper border, and, 

 following the contours of the shell, become split up into twos and threes, which re- 

 unite into a simple large fold terminating in the posterior part of the upper 

 border. The rugae become very greatly dilated and widely separated on the 

 dorsal slope, and all over the rugae and sinuses are close, fine, concentric lines of 

 growth. Shell very thin. 



Dimensions. — Plate XXXIII, fig. 16, a specimen in the Grosvenor Museum, 

 Chester, measures — 



Antero-posteriorly . . . . 100 mm. 



Dorso-ventrally . . . .57 mm. 



Laterally . . . . .30 mm. 



The specimen is somewhat too narrow in the last diameter owing to the 

 overriding of the valves on each other. 



Localities. — England : the Carboniferous Limestone, North Riding, Yorkshire 

 (the specimens in the York Museum are labelled Wensleydale) ; and Halkyn 

 Mountain, North Wales. 



Observations. — I have founded this species on four very fine examples, one of 

 which, fig. 16, PI. XXXIII, is in the possession of the Grosvenor Museum, Chester, 

 and was "obtained from Halkyn Mountain; one other, fig. 7, PI. XXXIV, is in the 

 collection of Mr. Joseph Wright, of Belfast, and is labelled North Riding, York- 

 shire. It was presented to him by the late Mr. E. Wood, whose name was given 

 to the genus of Crinoids, Woodier inus. It is unfortunate that the exact bed of 

 limestone whence it was obtained cannot, therefore, be located, but it most 

 probably was obtained from one of the beds of the so-called Yoredale Limestones, 

 which are, in my opinion, only the local representatives of the upper part of the 

 Carboniferous Limestone of Derbyshire. Both specimens possess the two valves, 

 and are fine casts of the exterior, but Mr. Wright's specimen is incomplete near 

 the umbones, and shows the characteristic ossicle in section. 



Two other specimens labelled Wensleydale are in the York Museum (Reed collec- 

 tion [Wood]). It appeared to me at first that possibly this species was only a 

 giant form of E. sulcata; but, though in general characters coming closer to that 

 species than to any other of the genus, E. expansa has, in the young stage even, 

 the double ribs in the central part of the shell much closer than in that species, 

 and it is also comparatively much less transverse. 



In size E. expansa approaches E. primseva, but the latter species has not the 

 well-marked ribs and sulci, and is comparatively much broader in its dorso-ventral 

 diameter. 



