142 CARBONICOLA, ANTHRACOMYA, AND NATADITES. 
tion, retaining the name Avicula, and this probably is the reason why he describes in 
the same volume a shell (Modiola producta) which from his figure I take to be the 
same as Sowerby’s form. It is said to occur in coal shale at Wakefield, but no 
notice is given in the description of any definite shape or characteristics. The 
posterior end of Captain Brown’s specimen was imperfect, so that it is impossible 
to give a dogmatic opinion as to the real nature of the shell. In my opinion it 
was either a large form of N. carinata, or more probably a specimen of 
N. quadrata. 
With regard to the American specimens, I am judging from figures and 
descriptions only, for I have been unable to obtain access to forms from Missouri 
and Illinois. The figures and descriptions, however, show such a close connection 
with British forms that I have ventured to place Myalina subquadrata and 
M. meliniformis as doubtful synonyms of Sowerby’s species N. quadrata. 
‘his form is comparatively rare; it occurs on an average of only one to a 
hundred of the other species in the Hard-mine of North Staffordshire. The charac- 
teristic flattened U-sbaped form with a much expanded posterior wing separate it 
from other species. The oblique ridge, too, is more nearly at a right angle to the 
hinge-line. It is connected with N. modiolaris on the one side and Naiadites 
carinata by a series of intermediate examples, forming with the three foregoing 
species one natural group which appears to be developing into four different 
distinct forms, characterised mainly by changes in the rate of growth of the shell 
at different points, the concomitant variations in anatomy depending on this. 
5. Narapires evoneata, Hind, 1883. Plate XVIII, figs. 22, 26—35. 
Natapires ELONGATA, Hind. Quart. Journ. Geol. Soc., vol. xlix, p. 256, pl. vu, 
figs. 15, 15 a, 16, 17, 1883. 
Non = —- Dawson. Acadian Geology, Ist edit., p. 43; 2nd edit., 
p- 202, fig. 43. 
Specific Characters.—Shell tumid, modioliform, transversely elongated, only 
slightly equivalve. The anterior end is short and swollen, the posterior obliquely 
tumid below, flattened and compressed above so as to become concave between the 
hinge-line and the oblique gibbose keel, which passes downwards and backwards 
from the umbones to the posterior inferior angle, preserving its form, though 
somewhat expanded and less elevated to the edge of the shell. The anterior end 
has a blunt convex border, continuous with the inferior border, which is straight 
and directed downwards and backwards, having the byssal notch about the middle 
