AMMONlTlDxE, 63 



A. Dorsal portion of lohorls rounded^ not keeled. 



1. Fimbriati. Oolitic. ^.yim6?-ia^iis, cl'Orb. (xxxiii, 45, 46). 



2. Planulati. Jura, Chalk. ^. an?iii/aiii«, Sowb. (xxxiv, 47, 48). 



3. Ligati. Cretaceous. A. ligatus^ d'Orb. (xxxiv, 49, 50). 



4. Globosi. Alpine Trias. 



5. Heteroph^'lli. Jura, Alpine Trias. A. hete7'02Jhyllus, d^Orh. 



(xxxiv, 51, 52). 



B. Whorls dorsally flattened. 



6. Capricorni. Jura. ^. caprico?v?.u.s', Schlotli. (xxxiv, 54, 55). 

 t. Armati. Jura. A. longispinus, Sowb. (xxxiv, 56, 58). 



8. Coronarii. Jura, Chalk. A. Blagdeni, Sowb. (xxxiv, 57, 59). 



9. Macrocephali. Jura. A. Herveyi^ Sowb. 



10. Compressi. Chalk. ^. 5eaMmo??^rani<,s-, d'Orb. (xxxiv, 53, 60). 



G. Dorsally channeled. 



11. Dentati. Jura, Chalk. ^.marrji7/a?^is-, Schlotli. (xxxv, 61,62). 



D. Dorsally keeled, keel entire. 



12. Arietes. Lias. yl. Z)^yVo?^s, Brug. (xxxv, 63). A.bisulcatus, 

 Brug. 



A. serpentinus, Schloth. (xxxv, 65, 66). 

 A. cristatus, Deluc. (xxxv, 67). 

 Dorsal keel crenated. 

 A. cordatus, Sowb. (xxxv, 68, 69). 



16. Rothomagenses. Chalk. J[. ro^/io^nag'en.sis, Brong. (xxxv,70). 



F. Dorsally sharp-edged. 



17. Disci. Chalk. A. Metternichii, Hauer (xxxv, 71'). 



Prof. Alpheus Hyatt, in his article on " Fossil Cephalopods," 

 published in the Bulletin of the Museum of Comparative Zoology, 

 i, 71, regards the Ammonoids, including all the cephalopods 

 with serrated or foliated septa, the Clymenife, Goniatites, Cera- 

 tites, and Ammonites proper, " as a distinct order from the 

 Nautiloids and Dibranchiate Cephalopods :" the typical group 

 of this order being the so-called genus Ammonites. This en- 

 larged view of the systematic position of the Ammonoids is by 

 Prof. Hyatt attributed to Prof. Agassiz, but it is evident that 

 von Buch had a glimmering of the same idea, because his groups 

 (mainly those I have enumerated above), although permitted by 

 him to remain under the generic name Ammonites, were desig- 

 nated as " families." Prof. Edward Suess, also, regarded the 

 genus Ammonites as a family, the typical groups of which were 

 of generic rank ; and recently Dr. Paul Fischer adopts for them _ 

 tlie order Ammonea. 



Prof. Hyatt reverses the use of " dorsal" and " abdominal " 

 in his descriptions of the shells; inasmuch as the animal of 

 Nautilus and Ammonites is placed with its abdominal side to 

 the periphery of the shell, he calls this outer side of the latter 

 " abdominal," and the inner or sutural side " dorsal." I regard 



13. 



Falciformi. Jura. 



14. 



Cristati. Chalk. 





E. 



15. 



Amalthei. Jura. 



