AMMONITID^. 85 



Cretaceous, with the exception of Scaphites, Turrilites and 

 Baculites. Neumaja' has divided them into two groups : Ham- 

 ites, applying to the species approaching Lytoceras b}^ their 

 ornamentation, and their sutural line having lobes symmet- 

 rically divided into pairs ; Crioceras, containing the forms 

 having the ornamentation of Acanthoceras, with lobes not sym- 

 metrically divided. Fischer arranges them in the following sub- 

 genera or sections, some of which are considered genera by 

 other systematists : 



MACROSCAPHiTES, Meek, 1816. Shell with inner turns merely 

 in contact, or so slightly embracing as to leave a very large, 

 shallow umbilicus ; periphery rounded ; body portion much ex- 

 tended from the inner volutions ; surface costate. S. gigas, 

 Sowb. 



ANCYLOCERAS, d'Orb., 1842. Shell at first spiral, discoidal 

 with separated whorls ; afterwards produced at a tangent and 

 then bent back again upon itself like a hook. 41 sp. Infer. 

 Oolitic, Cretaceous ; Europe, South America, United States. H. 

 spinigerus, Sowb. (xxxii, 33). Gault, Folkestone. 



ANisocERAS, Pictet, 1854. Shell at first spiral, helicoid, whorls 

 separated, at length more or less prolonged and reflected ; trans- 

 versely ribbed ; sutures of septa with five lobes and saddles, all 

 bipartite. 12 sp. Gault to Upper Greensand ; Europe. Creta- 

 ceous, Jurassic; India. H. Saussureanus, Pictet (xxxii, 84). 



HAMiTES, Parkinson (restricted). Shell conical, hook-shaped, 

 bent upon itself more than once, the courses separate. 38 sp. 

 Chalk ; Europe, S. America. 



HAMiULiNA, d'Orb., 1849. Differs from Hamites in being only 

 once bent upon itself, not in contact. 20 sp. Neocomian ; France. 

 Gault (?); India. H. trinodosa^ d'Orb. (xxxiii, 42). 



PTYCHOCERAS, d'Orb., 1840. Shell bent once upon itself; the 

 two straight portions in contact. 8 sp. ISTeocomian to Creta- 

 ceous ; Europe, India, United States. H. Emericianus, d'Orb. 

 (xxxiii, 43). France. 



DiPTYCHOCERAS, Gabb, 1869. Three straight limbs in contact. 

 A Ptychoceras in every respect except that it has an additional* 

 limb which incurves, enveloping both the preceding to a slight 

 degree only. Meek considers it doubtfully identical with Ptycho- 

 ceras. 



ToxocERAS, d'Orb., 1840. (Toxon, a bow, ceras, a horn.) Shell 

 horn-shaped or curved ; the six lobes and saddles of the sutures 

 simply crenulated ; last chamber large. Connected with Crio- 

 ceras and Ancyloceras by numerous intermediate forms. 20 

 sp. Neocomian ; France. H. bituberculatus, d'Orb. (xxxii, 32). 



CRIOCERAS, Leveille, 1836. Shell discoidal, whorls not contig- 

 uous, but in the same plane. 13 sp. Neocomian to U. Green- 

 sand ; Europe. Some of the species are believed to be merely 



