393 



AMMONOIDEA 



CHAP. 



short, sutural line undulated, simple. Principal genera : Cly- 

 donites, Choristoceras^ Rhahdoceras, Cochloceras. — Trias. 



Fam. 6. Pinaeoceratidae. — Shell discoidal, usually smooth, 

 body-chamber short, sutural line very complex, lobes numerous. 

 Principal genera : Pinacoceras^ Sagecera%. — Carboniferous to 

 Trias. 



Fam. 7. Amaltheidae. — Shell broad, keeled, last whorl con- 

 cealing most of the spire, sutures with auxiliary lobes, incised. 

 — Principal genera: Amaltheus, Schloenhacia^ Sphenodiscus. — 

 Trias, Cretaceous. 



Fam. 8. Ammonitidae. — Body-chamber long, whorls narrow. 



s — 



Fig. 258. — Various forms of Ammonoidea : A, Goniatites crenistria J. Phil., Carb. 

 Limestone; B, Ceratites nodosus de Hann., Muschelkalk; C, Ammonites {Parkin- 

 sonid) Parkinsoni Sowb., Inf. Oolite ; D, Phylloceras helerophyllum Sowb., Upper 

 Lias; s, «> sutural lines. 



uncovered, more or less ribbed, aperture simple, sutural line 

 normal, aptychus single, corneous. Principal genera : Ammonites^ 

 Aegoceras. — Principally Lias. 



Fam. ^. Lytoceratidae. — Shell discoidal, body-chamber short, 

 aperture simple, no aptychus. Principal genera : Lgtoceras, 

 Phylloceras (Fig. 258, D). — Trias to Cretaceous. 



Fam. 10. Harpoceratidae. — Shell discoidal, compressed, 

 margin keeled, surface with straight or arched ribs, aperture 



