ON PTEROMYA CROWCOINIBEIA MOORE AND SOME SPECIES OF PLEUROMYA 
AND VOLSELLA FROM THE PHYTIC AND LOWER LIAS. 
BY L. RICHARDSON, F.R.S.E. AND J. W. TUTCHER. 
[Plates VIII. and IX.] 
For a number of years past we have been engaged in studying the 
Rhsetic and basal Lower-Lias deposits of Gloucestershire and Somerset. 
In the course of our investigations we have collected many specimens 
of Pleiiromya and Volsella. Of these some could be readily identified 
with already-described and figured forms, but of the others, some 
appeared to be undescribed and others to be known b)^ names that 
obviously required investigation. 
The present paper is the result of our examination of the specimens 
we have collected. 
THE GENUS PTEROMYA MOORE. 
This genus was created by Charles Moore for the reception of such 
inequivalve Myadce as his species croivcomheia.'^ It does not appear to 
have been generally accepted, but as he created the genus, and as the 
feature upon which he mainly founded it, namely, the inequality of 
the valves, is very distinctive, we are of opinion that it ought to be 
used. 
PTEROMYA CROWCOMBEIA MOORE. 
Plate VIII., figs, la, b, and 2. 
1861. Quart. Joxrn. Geol. Soc, Vol. XVII., p. 506, plate xv., 
figs. 22 and 23. 
Remarks. — Moore's type came from the Flinty Bed of Beer Crow- 
combe, which is equivalent to the Pleurophorus-l^ed of Blue Anchor. f 
Typical specimens, however, have only been found in abundance — and 
in great abundance — in bed 21 at Blue Anchor. J 
Moore, in his description, refers to the posterior ridge and area on 
the left valve,, but when describing the rigJit valve — whilst commenting 
* Quart. Journ. Geol. Soc, Vol. XVIL (1861), p. 505. 
t Quart. Journ. Geol. Soc, Vol. LXVII. (1911), p. 17. 
t Id., p. 17. 
