NAUTILIDA. 
bl 
large reduction to be made in the number of generic forms at 
The following synopsis will exhibit these 
variations in some of the more important genera. 
present accepted. 








AMMONITID. 
Form oF SHELL. NavuTILip&. 
With Sutures Sutures 
| undulating | toothed at complex lobed 
| sutures. the base. | or foliaceous. 
Stra b! ierikleis tha e.td Orthoeeras.s «.\| -1scdseeek «s Baculina. Baculites. 
Bactrites..... Wer auaaet Shiela = abe iNvacporete . |Rhabdoceras 
GOMPNOCELE sate =4 ke sjelele|\s/esieye obras [SESSA Se 
Bent or curved....... Wy RtOCerasace)latie ercle oileele bibs cula con Toxoceras. 
Phragmoceras |)... vessese[i eer see. WAS Settee tats 
Discoidal spire and) (/|/Ascoceras ....).-.--056-<s|.000-+0-- |[s,ateteroteteiere rend 
free whorls....... { CYLOCHLAS «4. 5|| jo pte = jefe) ame were Cryoceras. 
Ibid. Finally straight | | 
or hook-shaped. ...|Lituites...... cee Bet or Pepil| aya sales ohare Ancyloceras 
Hook-shaped or bent 
uponitselfmore than 
ONG, s WHOEIS| LECO si | sje: oyeie-e ord J» «0040 Wee atekcr st cus teoull inde Ope orca ‘Hamites. 
Tbid. Straight portions | 
ME COMLAC trapeioterercesteroiellVeisstefele leet (= *ai> Peo Cece ‘Ptychoceras. 
Involute, spiral...... Nautilus.” 2: Goniatites..|Ceratites. Ammonites. 
Nothoceras....|...+- a ieitistenri| ehcror eae 6 ave aca Grate 
EIA FILS (Clymenia.. Beas Shore aera ican orate 
OBOE Te Oe Wass easieays = l|'<« « vereise | OLY CQOMILGR. 
Involute; last cham- 
ber detached, hook- 
shapeders kth. FARE Sale eT Ae AEA Ap aot OG ISS AeOe Scaphites. 
Elongated, spiral, 
whorls im icomtacts. o/s. se +1). 216 af lenctctay shepaeeit, oas;| oreuaye ops 683 Turrilites. 
Stic DOECO OO COE lise ced thevsins| sono ccc ¢| CObDLOCETAS: 
Spiral, elongated, | 
whorls not incontact|Trochoceras ..|........68.|.eeeeeeee Helicoceras. 
Spiral, elongated, the 
last whorl free, pro- 
Cucedia Md ere cui yes eya: eset, x19 cer ey-rsiarlis,«10 sr eysepereretall Peyod «(ac0.0 Heteroceras. 



lania, Bayle, 1878. 
Distr.—Fossil, 1200 sp. 
Australia, Europe. 
naliculatum, Sandb. 
Famity NAUTILID A. 
OrTHOCERAS, Breynius, 1732. 
Etym.— Orthos, straight, and ceras, a horn. 
Syn.—Actinoceras, Bronn, 1835. Orthoceratites, Breyn. Jovel- 
Cycloceras and Loxoceras, M’Coy, 1844. 

L. Silurian to Triassic; N. America, 
O. subannulare, Barr. (xxix, 79). O. planica- 
(xxviii, 67). 
Shell straight, aperture sometimes contracted. 
Probably the animal was not able to withdraw itself completely 
