HELICIGONA ARBUSTORUM. 421 
The ODONTOPHORE or radula is of the usual oblong shape, about 6 mill. long 
and 2 mill. wide, bearing 120 or more slightly oblique transverse rows of teeth, 
each row composed of about 79 or more denticles arranged bilaterally in three series. 
The median row is constituted by a longitudinal series of symmetrical obscurely 
trifid teeth, of which the mesocone is strong and powerful while the acute ecto- 
conic points are but slightly developed. ae 
Fic. 481.—Representative denticles from the radula of Helicigona arbustorum, Selby, Yorks. 
(based ona photograph by Mr. W. Bagshaw of a preparation hy Rev. Prof. H. M. Gwatkin). 
The laterals are about twenty in number and bicuspidate, they have a wide 
basal plate of attachment, but as usual are deficient of the inner angle, and they 
resemble the median row in possessing a strongly developed mesocone which is 
asymmetrically placed on account of the complete atrophy of the endocone and the 
increasing development of the ectocone. 
The marginals are nineteen or more in number and are indicated by the bifur- 
cation of the mesoconic point and the comparative increase in the size and importance 
of the ectocone, which towards the outer margin tends to become bifid also, but 
occasionally the extreme outer marginals are simply acicular. 
The formula of a Selby specimen, collected by Mr. J. F. Musham and prepared 
by Rey. Prof. H. M. Gwatkin, is 
Ae + FP + $442 +3) x 120 = 9,480 teeth. 
Reproduction and Development.—Although the amorous coquet- 
ings of this species have apparently never been observed or chronicled, 
yet Mr. Guy Breeden has observed and photographed the congress of this 
species, showing the shells during the act as arranged side by side, and the 
fore-part of the animals turned towards each other, so that their right sides 
were somewhat approximate, the interlaced exserted organs visibly con- 
necting them together. ‘lhe pairing season has been noticed to extend 
from the beginning of April quite into the autumn months, while the 
type form has been observed mating with the var. favescens and even in 
congress with Helix nemoralis, but no record has been made of the results 
of such unions. ‘The seminal element is transferred by means of the 
spirally twisted or corkscrew-shaped spermatophore, which after pairing 
becomes lodged in the spermathecal diverticulum of the companion snail 
where it speedily disintegrates. 
The eggs, which are laid in small clusters at the roots of Coltsfoot and 
other plants, are thirty to fifty or more in number, spherical in shape, and 
of an opaque yellowish colour, though semitransparent when deposited. 
They are about three mill. in diameter, and laid from April to September, 
being said to hatch in fifteen to twenty days, passing the winter in the 
immature stage, young shells being usually plentiful during the autumn 
months, attaining their full growth in the following spring and summer 
months. During the growth and development of the shell and prior to the 
rest periods, the free edge of the aperture of the shell may be thickened 
at each cessation of growth by a somewhat yellowish-white calcareous 
deposit or submarginal rib, as in //. pisana, which in the adult show 
externally as transverse yellowish bands encircling the whorls and desti- 
tute of the mottled markings and band characteristic of the species. 
