the Lingual Dentition in the Gasteropoda. 241 
pavement, as in Janthina or Scalaria, or in the pleure of a 
lingual ribbon, as in Atlanta and Carinaria. There are, how- 
ever, mixed characters in the dentition of some genera; and 
the subject requires much careful study to elicit all that may 
be deducible from it as a guide to classification. 
It would be very desirable to establish a fixed nomenclature 
for the parts, and some uniform mode of description of the 
lingual apparatus, so that the dental characters of any species 
referred to the fixed types shall be definite and unequi- 
vocal. 
I have already employed Prof. Huxley’s excellent name 
“ odontophore”’ for the tooth-bearing membrane, with its ex- 
panded ale in front embracing the tip of the tongue and being 
continuous with the lining membrane at the sides of the oral 
cavity, the posterior tubular portion of this organ, named 
the lingual sac, carrying the teeth upon its floor, extending 
backwards to the closed extremity containing the dental pulp 
or formative matrix, and forwards over the tip to the frenum 
of the tongue. The upper wall of the lingual sac terminates 
anteriorly in a crescentic fold, by which it becomes continuous 
with the lining of the cesophagus. The fore part and body of 
the tongue proper is supported by lateral cartilages wrapped 
together by muscle and ligament at the mesial line, and often 
having smaller supplementary pieces moveably articulated in 
front, as in the Zurbos and Nerites. The cartilages in the 
carnivorous families in particular conjointly form a grooved 
surface, over which the odontophore glides when in action. 
The common dental area or the space occupied by the teeth is 
usually divided into three lesser longitudinal areas, a central 
and two lateral, commonly known as rachis and pleure. The 
latter name may be retained; but the “ central dental area,” 
though longer, is preferable to “rachis,” which is not sufti- 
ciently definite. 
The central area usually presents a median series of dental 
plates, either alone or with one or more lateral series. The 
median series, however, is often suppressed. The pleura may 
present one, two, three, or many longitudinal rows of teeth ; 
and these are numbered, from within outwards, first, second, 
third, &e. 
With what has been already said of the basal plates and 
dental processes connected with them, this brief anatomical 
sketch will answer all practical purposes. The special types 
of dentition will be noticed when the groups or families which 
they characterize come under consideration. 
Having completed the foregoing introductory remarks, | 
