FF. R. 0. Reed— Woodwardian Museum Notes. 249 
I11.—Woopwarp1an Musrum Nortss. 
AxsnormMalL Forms oF Sprrirera Liveara (Martin). 
By F. R. Cowrzer Rexp, B.A., F.G.S. 
(PLATE XI.) 
SERIES of specimens showing successive stages in the develop- 
ment of a remarkable malformation of this species seems to 
me quite worth recording. ‘The specimens are all from the Car- 
boniferous Limestone of Settle. 
The normal and common form of Spirifera lineata is well-known ; 
and its varieties—Sp. imbricata of Sowerby, Phillips and McCoy, 
and Sp. elliptica of Phillips are likewise constantly met with in the 
Carboniferous Limestone. The wide gaps between the typical form 
and its varieties can be bridged over by the examination of a large 
series of individuals, so that Davidson has grouped these three 
forms under one specific name. 
The variation from the typical form Sp. lineata occurs in two 
directions ; first, in the surface ornamentation, by the thickening and 
widening of the concentric lines on the exterior of the valves, until 
they become the well-marked flattened lamelle of Sowerby’s Sp. 
imbricata; this change is also accompanied by the production of 
longitudinal fimbriations which are foreshadowed by fine strive in 
some specimens of the typical form. 
The second direction in which variation occurs is in the shape 
of the shell; from subcircular it becomes transversely elliptical ; 
and the surface of the dorsal valve is ridged up into a longitudinal 
mesial fold, while a corresponding sinus is formed in the ventral 
valve, as seen in Sp. elliptica. There are transitional forms to be 
found in this case also, showing intermediate characters. 
In some species of Sp. imbricata I have also noticed a tendency 
for the shell to become somewhat transversely oval. It is thus 
clear that in this species there is a great range of variation from the 
typical form, but in addition to these normal varieties I have recently 
detected in the Woodwardian Museum a number of specimens 
showing stages in the development of an abnormal yet nearly 
symmetrical and regularly occurring deviation. They exhibit the 
following characters :— 
(1) A tendency to become transversely elliptical without acquiring 
the surface ornamentation of fine strize found in Sp. elliptica. 
(2) The development in the ventral valve of a mesial furrow of 
peculiar form. The normal ventral sinus which sometimes occurs 
in this species is broad, rounded and shallow, and runs from near 
the beak to the front edge of the shell, causing a gentle and regular 
sinuation of the margin. 
In these peculiar individuals, however, the mesial furrow com- 
menees irregularly as a short indentation, which is continuous and 
of equal depth, extending in some cases nearly from the umbo to 
the front margin, or only from the middle of the valve ; or it consists 
of an irregular series of indentations of varying depth ; or it exists 
merely as a slight groove on the anterior border. 
