2*21 AM MOM , 



aw AMMONITES. Urn jr. 



Shell spiral, discoidal. more or lc involute: septa undulated, 

 the sutures lobed and foliated: siphunde dorsal: margin of 

 mouth sometime^ produced into one or more horns. 



About 700 species. Triassir. ( 'retaceous. X. tnnl K. America; 

 r, a rope ; India.; New Zealand. 



A.. OBTU8US. PL 101. iig. .~>:>7. I/ia^i-. Li/mr Iti-iji*. 



The young shell (litters much from older specimens in the 

 degree of involution and in bcinir '<'^ complicated in the sutural 

 lobes; even the external ornamentation varies, so that the above 

 number of described >pecies will probably be much reduced 

 upon careful revision. As an example. A. ttjH'iidcti* from the 

 greensand, Cambridge, Kng.. according to .Mr. Seeley includes 

 fourteen other so-called species from the same bed ; and A. />!<in- 

 t/lntux may include five species. 



Ammonites have been discovered in the high passes of the 

 Himalaya Mountains, over Hi. 000 feet above the sea. 



The nominal species being so numerous, it has been usual 

 until recently to class them in the following artifical groups: 



A. Dorsal portion of whorls rounded, not keeled. 



1. Fimbriati. Oolitic. A. FIMBRIATUS, d'Orb. PL 101, ligs. .->:js. :>:','.. 

 -.'. I'iaimhiti. -Inra, Chalk. A. ANNULATUS, Sowb. PI. 102, ti^s. ."i-Mi, o41. 



3. Ligati. Cretaceous. A. LIGATUS, d'Orb. PI. \\^. li^s. r>4i2, .")4:J. 



4. (ilobosi. Alpine Trias. 



"'. Hetei^phylli. Jura, Alpine Trias. A. HETEROPHYLLUS, d'Orb. 

 PI. 102, ti.u-s. :,M, 545. 



B. Whorls dorsally flattened. 



<;. ( apiicorni. .Jura. A. CAPRICORNUS, Schloth. PL K)'J, ti-s. ."4<i, r 47. 

 7. Annati. Jura. A. LONGISPINUS, Sowb. PI. 102, figs. 54s, r4i. 

 s. Coroimrii. Jura, Chalk. A. BLAGDRNI, Sowb. PL 10^, li-. ")")(), .V>|. 

 9. Macrocephali. Jura. 'A. HERVEYI, Sowb. 



10. ( nupressi. Clialk. A. BEAUMONTIANUS, d'Orb. PL 102, tigs. r>.VJ. .~M:J. 



C. Dorsally channeled. 



11. Dentati. .Jura, ( luilk. A. MAMILLARIS, Schloth. PL 10:5, lig. .').> 4, -Vi.">. 



D. Dorsally keeled, keel entire. 

 \'l. Aii.tcs. Lias. A. BIFRONS, Brug. PL 103, fig. ."i56. A. BISUL- 



CATUB, Brag. PL 10:;, n u . 



I:}. F;il<'i!uniii. .Inra. A. 8ERPENTINU8, Scliloth. PL 108, ligs. -V)H, .~i51>. 

 1 I. < ristuti. Clialk. A. CRI8TATU8, Deluc. PL 10:5, fig. T.C.O. 



