AMMONITID. 63 
A. Dorsal portion of whorls rounded, not keeled. 
Fimbriati. Oolitic. A. fimbriatus, d’Orb. (xxxiii, 45, 46). 
Planulati. Jura, Chalk. A. annulatus, Sowb. (xxxiv, 47, 48). 
Ligati. Cretaceous. A. ligatus, d’Orb. (xxxiv, 49, 50). 
. Globosi. Alpine Trias. 
. Heterophylli. Jura, Alpine Trias. A. heterophyllus, d’Orb. 
(xxxiv, 51, 52). 
B. Whorls dorsally flattened. 
6. Capricorni. Jura. A. capricornus, Schloth. (xxxiv, 54,55). 
q. Armati. Jura. A. longispinus, Sowb. (xxxiv, 56, 58). 
8. Coronarii. Jura,Chalk. A. Blagdeni, Sowb. (xxxiv, 57, 59). 
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. Macrocephali. Jura. A. Herveyi, Sowb. 
. Compressi. Chalk. A. Beaumontianus, V’Orb. (xxxiv, 53, 60). 
CO. Dorsally channeled. 
11. Dentati. Jura, Chalk. A. mamillaris, Schloth. (xxxv, 61,62), 
D. Dorsally keeled, keel entire. 
12. Arietes. lias. A. bifrons, Brug. (xxxv, 63). A. besulcatus, 
Brug. 
13. Falciformi. Jura. A. serpentinus, Schloth. (xxxv, 65, 66). 
14. Cristati. Chalk. A. eristatus, Deluc. (xxxv, 67). 
E. Dorsal keel crenated. 
15. Amalthei. Jura. A. cordatus, Sowb. (xxxv, 68, 69). 
16. Rothomagenses. Chalk. A. rothomagensis, Brong. (xxxv,70). 
F. Dorsally sharp-edged. 
17. Disci. Chalk. A. Metternichit, 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 Clymenie, 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 
the 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 
