THE CEPHALOPODA. 



181 



forming deep angular sinuses without denticulations, with a prominent siphonal lol)e 

 (figs. 34, 35, 36). An extensive genus, containing many species, distributed from the 

 Sihu-ian to Triassic strata. Ex. Goniatites Orhic/nyanus, d'Archiac (fig. 35). 



2. Family Ceratitid^, Mojsisovics, 1879. — Shell spiral, discoidal; septa undulate, 

 with denticulate borders. 



Genus. — Ceratites, Be Raan, lS'2^i. Shell spiral, discoidal; whorls contiguous, 

 convolute. Septa undulating, but not ramified, with denticulate borders. Siphonal 



Fig. 37.— Side view. Fig. 38 ■ 

 Ceratites nodosus, De Haan. 



Fig. 39.—Ceraliles Robini, 

 TliioUiere. 



Ceralites aeinipart'ttus, 

 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. nodosus, De Haan (fig. 37) ; C. Robini, 

 ThioUiere (fig. 39). C semipartitus, von Buch (_tig. 40). 



3. Family Ammonitice, OiDen, 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, with 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). Srd. 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 we examine an Ammonite in which the 



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