119 
AMMONITES Heterophyllus. 
TAB. CCLXVI. 
Sp. Cuar. Lenticular, umbilicated, striated ; sinu- 
osities of the septa of two kinds, small and 
acuteangular, or large and ovate. 
Tis is one of those Ammonites with the inner whorles 
concealed, which have often been called Nautili, but 
which an attention to the edges of the septa will always 
distinguish. Ithas the front rounded, the sides convex 
marked by very numerous diverging, elevated, and 
slightly. waved, striz ; the umbilicus small and deep ; 
the apperture elliptical with a notch for the reception of 
the preceeding whorle, it is nearly two thirds the diame- 
ter of the shell in length. The edges of the septa are 
deeply sinuated and some of the sinuses are larger than 
others and much more obtuse so that the lines formed by 
them upon the surface of the cast, resemble two kinds of 
pinnated foliage, in one of which the terminal leaflets are 
oval and large, while in the other the divisions are all 
small and have acute points. 
We have named this Ammonite after a configuration 
that in the specimen before us has been rendered remark- 
ably distinct by the decay of the surface; in whatever 
state it occurs, however, sufficient traces of the edges 
of the septa may generally be found to show the cha- 
racter, unless the surface be very deeply eroded, for 
the shell itself is thin and adheres but slightly to the 
septa. Itis often necessary to take into consideration 
L3Y0 
