EURYDONTOPIIOROUS TEETH. 
269 
Tliis type of tootli is possessed by Phjjsa faiitinali.^, and its 
characters may be broailly expressed by the formula 
X 57=19,893. 
The genus Chilina, a primitive group of fluviatile snails inhabiting 
South America, has teeth of the same general character, bearing a 
similar knobbed enlargement of the anterior end of the base of 
attachment and the transverse rows of teeth having the same anteriorly 
directed arrangement. 
The Eurydontophor.v bi’oad ; oSois, tooth ; to bear) 
are those species with teeth characterized by a somewhat square base 
of attachment to the radular membrane, 
and distinguished from the Aculeate 
type of teeth by their gradual diminution 
in size, in proportion as they recede 
from the centre of the membrane, their 
greatest development being near the 
centre — perhaps in correlation with the 
median longitudinal ridge upon the 
lingual cartilage, which probably endows 
the teeth thereon with increased func- 
tional importance, and leads to their 
acquiring greater strength than those 
less favourably placed for the efficient 
exercise of their powers. 
The teeth are usually divisible into three series, distributed upon a 
central, two lateral, and two mar- 
ginal areas ; the lateral and marginal 
areas, however, often blend so in- 
sensibly together that no distinct 
line of separation can be made out 
between them ; this doubtful space 
bears teeth of a similar undecided 
character, as they partake of the 
characters of both series and are known as transitional teeth. 
The Eurydontophora have usually numerous transverse rows of 
closely-set cuspidate teeth, a form especially adapted for the reduc- 
tion of vegetable food, and, according to the character of the individual 
teeth, may be tentatively arranged in four groups, viz., Pycnoglossa, 
Zeugoglossa, Myriaglossa and Dichogiossa. 
Fig. 537. — Transverse section 
through the buccal bulb of A^io- 
livtax a^restis (L.), x30, showing the 
form of disposition of the radula and 
radular cartilages (after Hanitsch). 
b.c. buccal cavity ; in, ventral 
muscles of buccal bulb; r.c. radular 
cartilages with superimposed radula; 
s,d. salivary ducts. 
Fig. 538. 
Fig. 539. 
Fig. 538. — Typical Quadrate or Eurydontate 
tooth as seen from above, highly magnified. 
Fig. 539. — Side view showing the reflection 
and cutting points, highly magnified. 
