398 



AMMONOIDEA 



CHAP. 



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

 donites^ Choristoceras, Mhabdoceras, Cochloceras. — Trias. 



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

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

 Principal genera : Pinacoceras^ Sageceras. — Carboniferous to 

 Trias. 



Fam. 7. Amaltheidae,' — Shell broad, keeled, last whorl cou 

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

 — Principal genera: Amaltheus, Schloenbacia, Spheno discus. 

 Trias, Cretaceous. 



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



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

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

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

 Lias; «, «, 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: Lytoceras^ 

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



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

 margin keeled, surface with straight or arched ribs, aperture 



