RUTOTIA. 
55 
2. Genus. — Rutotia, de EonincJc, 1885. 
These shells are described as smooth, oval or suborbicular, inequilateral, 
inequivalve, with an elevated and prominent umbo, undefined ears, a short 
anterior and obliquely prolonged posterior side, smooth or slightly striated 
surface, and a short, straight, linear, edentulous hinge. 
The genus was described from Carboniferous beds, but it seems to me 
that some foreign Devonian shells, referred to Inoceramus and Posidonomya, may 
belong to it. 
It is distinguished from Posidonomya by its smoothness and its prominent 
elevated umbo. 
1. Rutotia elliptioa, Whidborne, sp. PL IV, figs. 9, 9 a, 10; and PI. V, 
figs. 2—9. 
1889. Myalina elliptica, Whidborne. Geol. Mag., dec. 3, vol. vi, p. 79. 
Description. — Shell large, ovoid, convex, broader than long, oblique, rath 
inequilateral. Umbo prominent, incurved, rounded, sharp at the point, tending 
forward but facing slightly backward, situated nearly in the centre of the upper 
margin. Hinge-margin short, apparently excavate behind the umbo. Lunule 
small, deep, and indefinite. Anterior margin broadly and obliquely convex. 
Inferior margin short and very convex. Posterior margin gently convex. Contour 
of back roundly convex in the central parts, becoming steeper behind so as to be 
sometimes almost perpendicular to the posterior edge, and flattening out to the 
inferior and anterior margins, forming a small, slightly concave, undefined wing- 
about the supero-anterior corner. Hinge unseen. Surface smooth, with only a 
few very indistinct lines of growth. Shell-structure very thin. 
Size of single valves. — Length 32 mm., breadth 40 mm., depth 12 mm.; or 
length 35 mm., breadth 40 mm., depth 10 mm. 
Localities. — From Lummaton there are thirteen specimens in my Collection, 
and one in the Woodwardian Museum. From Wolborough there are six in 
Mr. Vicary's Collection and one in the Museum of Practical Geology. ' ' 
Bemarhs. — This is a very variable species, with few distinctive characters. The 
variation is chiefly seen in the width, the obliquity, the convexity, and the contour 
of the postero-superior part, which is usually steep but occasionally somewhat 
expanded. It would be easy to regard several of the shapes as specifically distinct 
if they occurred alone ; but, on comparing a number of specimens together, it is 
