THE CEPHALOPODA. 
181 
forming deep angular sinuses without denticulations, with a prominent siphonal lobe 
(figs. 34, 35, 36). An extensive genus, containing manj^ species, distributed from the 
Silurian to Triassic strata. Ex. Goiiiatites Orhignyanus, d'Archiac (fig. 35). 
2. Family CERATiTiDiE, Mojsisovics, 1879. — Shell spiral, discoidal; septa undulate, 
with denticulate borders. 
6^e;?«5.— Ceratites, De Ilaan, lS2b. Shell spiral, discoidal; whorls contiguous, 
convolute. Septa undulating, but not ramified, with denticulate borders. Siphonal 
Fig. 37. — Sirfe view. Fig. 38 — Back view. Fig. 39. — Ceratites Roiiai, Fig. 40. — Ceratites semipartitus, 
Ceraiites nodosus, De Haan. Thiollieie. von Buch. 
lobe deep, separated on the median line by a small saddle (fig. 38). The Ceratites range 
from the Triassic to the Cretaceous. Ex. C. oiodoms, ]3e Plaan (fig. 37) ; C. Rohini, 
Thiolliere (fig. 39). C. semipartitus, vou Buch (fig. 40). 
3. Family Ammonitid^, Owen, 1836. 
Shell external, spiral, bent or straight, the last chamber large for a dwelling-place. 
Siphuncle central on the external or ventral side of shell. The margins of the septa 
ramified, wdth deeply lobated borders, divided into six lobes. 1st. The siphonal (d, 
figs. 41 and 43), embraces the siphon, and divides into two arms, which are attached 
by a shelly layer to the siphuncular tube. 2nd. The two that adjoin are called 
the superior lateral lobes (l). 3rd. The two that lie beneath them are the inferior 
lateral (l'), which often are much developed and very complicated in the ramifications of 
their lobes (figs. 41 and 43). 4th. The lobe which rests upon the side opposite the 
siphonal lobe and siphon is the columellar lobe (v, fig. 46). Between this and the 
inferior lateral are several auxiliary lobes [a, a, a, a, fig. 43). Thus there are in 
each septum six primary, viz. one siphonal, one columellar, and four lateral lobes, also a 
variable number of auxiliaries. When Ave examine an Ammonite in Avhich the 
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