ALIMENTARY SYSTEM — ODONTOPIIORE. 
256 
'I’he Elasmognatiia (eXan-fm, a metal ])late; yi'a^o?, jaw) or 
Ai)pentlicnlate jaw is a tyiie whose great peculiarity consists in the 
development of a very large, somewhat sipiare accessoiy palatal plate, 
which extends j)osteriorly backwards upon the roof of the mouth ; it 
is of similar material and consistency and about two-thirds the width 
of the jaw itself, with which 
it exhihitscontinuity of struc- 
ture. 'I'he upper portion of 
the jaw is imbedded in the 
tissues, ami the free portion 
is characteristically horse- 
shoe shaped with a strong and 
jHiinted median projection. 
'I'he Elasmognath jaw is 
restricted in this country to 
the genus Sikt'uk'j, although 
our s])ecies vary somewhat in the character of the jaw itself, S/icriii&d 
r/('(/iiiis possessing a practically oxygiiath jaw uj)on which the 
])osteriorly projecting palatal a])i)endage is developed, while Hiicc.'nmi 
pntritt, in addition to the well marked median beak or rostrum, 
which is the characteristic of the oxygiiatha, also displays strong 
and distinct transverse radiate ridges, simulating those of the true 
odontognathous sjiecies. 
'I'he OnoNToi’iioRE ((VSoik', tooth ; </>e/><n, to hear), Radula, or lingual 
ribbon, is a tongue-like cartilaginous process iirojecting upon the 
door of the huccai cavity, and forming a somewhat ju'chensile 
apparatus, with its fi-ee surface covered with an immense number of 
minute, hackwardly directed teeth, arranged in regular longitudinal 
and transverse rows, and of strikingly different forms in the different 
genera and species, the whole resting upon the suh-radular membrane, 
which is continuous with the lining of the huccai cavity, and i)laced 
111)011 tlie two somewhat confluent odontophoral cartilages, which are 
clo.sely iiniteil in the median line by fibrous and muscular tissue. 
'I'he very general possession of this organ, in a very largo section of 
the mollusca, has led to the term (do.sso])hora., or tongue-hearing, 
l>eiug applied to the groups possessing it. 
'I'he Radula Sac, from which the radula is developed as a some- 
what tubular outgrowth, is an eiiithelial invagination of variable 
length in the median line of the iloor of the mouth or huccai cavity, 
Fig. 512 front view and Fig. 513 side view of tlie 
Appendiculate or F'dasmognatlioiis maiulible of 
SiH'ci/iea />Ntris (F.)> X --5, from Chrisicliurch, 
FlaiUs., showing tlie convexity of the jaw generally 
and llie strongly tlevelojied accessory palatal plate. 
