ORDER II AMMONOIDEA 589 
Calycoceras, gen. nov. Type C. (Amin.) navicularis, Sharp sp.; Metacanthoplites, gen. 
nov. (Fig. 1232). Type 
M. (Amm.) rhotoma- 
gensis, @Orb sp. Cre- 
taceous.. 
Family 35. Peroni- 
ceratidae. Similar to 
Mammitidae in general 
aspect and ornamenta- 
tion of adult stage, but 
young have a distinct 
keel and a coronate form 
with heavy tubercles. 
Costae generally dicho- 
tomous, and venter often 
has channels or smooth 
zones on either side of 
the keel. Sutural out- 
lines more complex than 
in Mammitidae. 
Peroniceras, Gau- 
thiericeras, Gross. ; Hy- ean 
strichoceras, gen. nov. ites Caan Rhotomagense, Defr. sp. Cenomanian; Rouen, France 
(Fig. 1233). Type H. 
(Amm.) Coupe’, Brongt. sp.; Dipolocerus, gen. noy. (Fig. 1234). Type D. (Amm.) 
cristatum, VOrb, sp. Cretaceous. 
Family 36. Prionotropidae. Young resemble some forms of Mammitidae, but 
have a crenulated keel at an early stage, which is persistent. Costae usually finer and 


Fig. 1234. 

Hystrichoceras varians, Sowb. sp. Dipoloceras cristatum, Deluc sp. Lower Cre- 
Quedlinburg, Saxony. taceous. 
more closely set, and tubercles smaller than in that family. Spines become very large, 
volutions more quadrate in section, and venter flat with prominent keel and channels 
until a late stage. Dorsal sutures reduced in discoidal forms to one pair of large 
saddles and one of incomplete lobes on either side of the antisiphonal. 
Prionotropis, Prionocyclus, Mortoniceras, Meek ; Schloenbachia, Neum. (Type S. 
Germari, Reuss.). Cretaceous. 
