ae 
312 HELIX PISANA. 
rically disposed longitudinal blades, which ate thin and translucent, and set at right 
angles to each other, their edges being split along their entire length and diverging 
to form distinct flanges, which are inclined to each other at an angle of about 150 
or 160 degrees, forming a longitudinally channelled termination to the edge of 
each blade, and disappearing somewhat gradually before reaching the apex of the 
dart, but ending quite abruptly and squarely about the middle of the basal ex- 
pansion, which is terminated by a distinct annulus, composed of from twelve to 
sixteen longitudinal rodlets, which are only formed on completion of the dart. 
The JAW is a well-arched structure, quite convex from front to back, and nearly 
two millimetres broad from side to side, with bluntly 
rounded ends; of a somewhat deep fawn colour, becoming 
brown in the thicker parts, and bearing two stout 
transverse and usually divergent ribs which strongly 
denticulate both the upper and lower margins, and are ie. 416 Cee 
always near the centre ot the mandible where a third rib py,777 jisane: Malena seX0) 
is frequently developed between the usual pair. from Jersey. 
The strength of the jaw and its degree of denticulation is, however, largely a 
matter of environment, and varies within certain limits in different districts.! 
The bicostulate mandible is the most common form oa 
in this country, although specimens with three ribs are TaN 
frequent and occasionally met with even in quite imma- iy 
ture shells, the ribs at this stage usually, however, only 
indent the lower or eutting margin. In France, Moquin- Fic. 417.—Jaw of a young 
Helix pisana Miiler, X 10, 
Ts scribes » <liverge > bicosti jaw as é f 
Yandon describes the divergently bicostate Ja AS A ieee 
characteristic of the species, but M. Girard states that 
in Portugal the bicostate mandible is restricted to immature individuals, and that 
all fully adult shells possess a tricostulate jaw. 
The RADULA is of the usual oblong shape, and about 5 mill. in length and 13 mill. 
in width, composed of 140 or more gently curving transverse rows of teeth, which 
diminish gradually in size towards the margins, where the rows exhibit a tendency 
to fureate, or short additional rows may be interposed at intervals; each row is 
constituted by about $7 teeth, consisting of a tricuspid MEDIAN tooth with a strong 
mesocone and asmall but distinet ectocone on each side ; the LATERALS are usually 
about sixteen in number and bieuspid, the endocone being lost and the ectocone 
Vente 
: Fic. 418.—Representative denticles from the radula of Hledtx pisana, Tenby, highly magnified 
(based on a photograph by Mr. W. Bagshaw of a preparation by Rev. Prof. H. M. Gwatkin). 
23- 
\6. 
becoming gradually stronger and more prominent as the teeth recede from the median 
line; the MARGINALS are about twenty-seven in number, and show a distinet bifur- 
cation of the mesocone, the ectocone being quite separate and distinet, and abont 
the thirtieth row also tending to become bifid, many of the teeth near the outer 
fringe being distinctly quadrifid. 
The formula of a Tenby specimen prepared by Rev. Prof. H. M. Gwatkin is 
So + U8 444-18 +35 ~ 140 = 12,180 teeth. 
Reproduction and Development.—Little is known of the amours 
or life history of this species, but, according to Dr. Gassies, congress takes 
place during June and July, and although Moquin-T'andon denies that a 
spermatophore is secreted by this species, the well-developed and glandular 
epiphallus would seem to emphatically controvert that statement, and 
render it almost certain that the fertilizing element is transferred during 
pairing by means of a perfectly characteristic spermatophore. 
The eggs are described as about one-and-a-half millimetres in diameter, 
oval in shape, and greenish or pearly-white in colour, with a slight invest- 
1 Monogr., vol. i., p. 239. 
