189 
AMMONITES constrictus. 
TAB. A. — Fig . 1 . 
Spec. Char. Depressed, radiated, armed with a 
row of acute tubercles on each side the front ; 
inner volutions concealed ; radii undulated, of 
various lengths ; aperture even, oblong, con- 
tracted by a blunt-edged inflected lip. 
In some varieties there are a few tubercles near the 
centre, the same have also larger tubercles near the 
front : the tubercles are always largest about the middle 
of the last whorl, and gradually diminish towards the 
mouth and the inner turns, where they are entirely want- 
ing ; on the contrary, the radii are most conspicuous on 
the inner whorls. There is a minute, apparently open, 
umbilicus. The mouth which is placed at an acute angle 
to the radii, is reduced to an oval form by an inflexion of 
the edge, and is so much contracted that the shape of its 
opening is not affected by the preceding whorl ; the edge of 
it is so bent that the closed partis placed nearly at a right 
angle to the remainder. The septa, the last of which lies 
about half a turn from the mouth, are much sinuated, and 
numerous. 
Casts only of this shell have as yet occurred, but they 
are so perfect, that they exhibit every thing that can be 
expected. The termination of the last chamber is a very 
striking feature ; it is met with in almost all the speci- 
mens. From St. Colombe, in Normandy. 
AMMONITES Gervillii. 
TAB. A*— -Fig. 3. 
Spec. Char. Gibbose, umbilicate, radiated ; a 
small portion of the inner whorls exposed ; 
radii sharp, bent, furcate ; aperture trans- 
verse, oblong, arched ; lip arched, sharp 
edged. 
— 
The thickness of this is rather more than half the dia- 
meter : the umbilicus is large, beautifully exposing the 
