56 HELICODONTA OBVOLUTA. 
abundant muscular coat, but no caleareous cells were detected ; the VAS DEFERENS 
is slender and generally shows an abrupt and very persistent sigmoid flexure, which 
is basally attached to the columellar muscle, before entering the penis-sheath ; the 
RETRACTOR is attached to the vas deferens, which thickens before joining to the 
penis-sheath, and though showing differences of size, ete., there are no apparent 
differences of structure, and therefore probably there is no epiphallus ; the PENIS- 
SHEATH is singularly voluminous, thick, but attenuate above, the vas deferens 
entering terminally. 
In the natural position when the animal is extended, the free oviduct from its 
commencement to the opening of the dart sac is bent in a sigmoid flexure, the 
spermatheca duct arising from its highest point ; the spermatheca, as is usual, lies 
against the oviduct, and the mucus gland is twisted round the S bend. 
The ALIMENTARY SYSTEM shows an excessively long GSOPHAGUS, with thick 
and bulky whitish salivary glands; the csophagus gradually merges into the CROP, 
which is apparently merely an expansion of it, and combined with the sroMACH, 
whose pyloric end is abruptly bent ; the GUT is of the usual triodromous character, 
the middle tract being somewhat capacious, and the rectal tract long and slender. 
The CEPHALIC RETRACTORS show an elongate central stem, attenuate at its 
insertion on the columella of the shell, and near the base giving off a muscular 
strand to the rectum, as well as the penial retractor, which arises from a point 
about one-third of the length from the distal end, agreeing in this arrangement 
with the primitive Australian genus Panda. The two tentacular muscles are 
given off almost subterminally, they are powerful muscular bands, and each divides 
to serve the ommatophore, tentacle, and lip of their respective sides ; the BUCCAL 
RETRACTOR is formed by the continuation of the main muscle, and just before 
reaching the buccal bulb it divides, each branch again bifureating before attach- 
ment thereto. 
The MANDIBLE or jaw is about one mill. from end to end, flatly crescentic in 
shape, and bluntly rounded extremities, of an amber 
colour, of rather delicate consistency, with thickened 
and darker areas most distinct medially and towards 
the ends, and showing one central and several longitud- 
inally parallel paler lines; there are a somewhat vati- 
able number of broad, flat, rather indistinet vertical Fic. 88.— Jaw of 1. obvo/uta 
ribs, which slightly crenulate the lower or cutting  (Miil.) (highly magnified) after 
margin, but do not extend quite across the jaw. amu Poomees by Mr. W. 
3agshaw. 
The RADULA is of the usual oblong shape, and consists of from about 145 to 170 
transverse rows of teeth, each row consisting of 71 to 91 teeth, and constituted by 
a median unicuspid tooth, about 13 or 14 unicuspid laterals, and about 28 bicuspid 
and tricuspid marginals, which at the extreme margins degenerate into simple 
chitinous bars. 
COA GiP aie =e 
Fic. 89. — Representative teeth from the radula of H. odvo/uta (Mill.), from Ditcham Wood, 
Hampshire, after a highly magnified drawing by Prof. Boycott. 
The formula of a Ditcham specimen, according to Prof. Boycott, is 
app esp setts 4 dy ders 4 dors + 25 x 160 = 14,240 teeth. 
3 
Reproduction and Development. — Few observations have been 
made upon the sexual congress of this species, but Mr. L. Dawes, who has 
carefully studied this species in confinement, found a pair in the act of 
conjugation in the early morning of June 27th, 1912; the animals were 
facing each other, but not in actual contact, except by their intromittent 
organs, which were united together over the heads of the snails ; he also 
verified that oviposition takes place from May to the end of June, the 
eggs being white and laid in clusters varying in numbers from 8-20, and 
