148 XEROPHILA VIRGATA. 
The RADULA is 24 mill. long and 13 mill. wide, of the usual type of ground 
snails, with ill-developed or absent endocones ; the median row of teeth are tricuspid, 
the laterals are bicuspid, having only the mesocone and the ectocone, and this is 
— ~ 2 ae 
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Ang et eae 
“ef 
Fic. 237.—Representative teeth of the radula of . wixgata Da Costa, from Chipstead, Surrey, 
prepared and photographed by Dr. E. W. Bowell, x 360. 
c. central or median series ; a. admedian or lateral teeth ; 7. marginal teeth. 
said to continue quite to the margin of the membrane, but speaking from my own 
observations of a few years ago, the marginals gradually become tricuspid by the 
acquirement of a third cusp due to the splitting of the ectocone. 
The formula of a Chipstead specimen, prepared and photographed by Dr. E. W. 
Bowell, is 
19 x a ar i af an Ar 1 cae —— (B20 teeth. 
Phylogeny and Ontogeny.—'hat the more primitive state of the 
NXerophile was possibly tetrabelous, and constituted by paired, double 
dart-sacs, is suggested by XY. 7talw still retaining two sacs, though in a 
transitional semi-combined form, with a couple of darts still present therein. 
In YX. virgata the dart apparatus is normally reduced to the simple 
single sac and its contained dart, but we find that under special conditions 
or towards the limits of its geographical range there is apparently a distinct 
tendency to atavism, shown by the retention of a more or less definite 
bilobation, implying a former more complete separation of the sacs. 
According to Moquin-T'andon, this bilobation is not unfrequently met 
with in the stunted and recessive var. maritima Drap. of the French 
coasts, and the same peculiarity was observed by the late Mr. C. Ashford 
in some specimens of the same variety from Corfe, Dorset. ‘he same careful 
worker detected the similar atavic character in some XY. variabilis from the 
Island of Malta ; while specimens collected by Mr. J. Bliss, M.P., in 
December, 1920, at San Stefano, near Constantinople, and examined by 
Dr. E. W. Bowell, all showed the same retention of this primitive feature. 
'l'o further strengthen this hypothesis it would be desirable to compare 
the organization in this respect of other specimens of the species from 
remote localities, and dissections should also be made of adolescent 
animals in which indications of the former presence of double dart-sacs 
would probably be more frequently detected than in the mature mollusk. 
Reproduction.—Though the preliminary coquetings leading up to 
conjugation have not been observed or published regarding this species, 
yet it is well established by many observations that the breeding season 
is during the late summer and autumn months, and that the male element 
is transferred in the form of a delicate, serrate and twisted spermatophore. 
M. Bouchard-Chantereaux, who has so carefully studied the life-history 
of this and many other species, says that it breeds in September and 
October, but there are many reliable observations of pairing as early as 
August, and this process is continued up to October, and even November 
in this country. 
The eggs are stated by Bouchard-Chantereaux and Gassies to be 40-80 
in number, white, slightly transparent, more or less spherical in shape, and 
