AMMONITID^. 81 



side of the peripheral, two half-round ones limited partly by the 

 preceding whorl. S. jDseudo-ancejJS^ Ebray. 



C(EL0CERAS, Hyatt, 1861. 



Distr. — C. centaurus, d'Orb. (xxxvi, 81, 88). Middle and 

 Upper Lias. 



Pilffi on the periphery bifurcated ; lateral pilse single or bifur- 

 cated with one external row of tubercles, occurring regularly on 

 each, or at intervals on widel}^ separated pilae. The j^oung are 

 very much flatter than the adults, and the sides consequently, 

 verj^ narrow. They are smooth for the first one or two whorls, 

 subsequently becoming tuberculated. The tubercles almost 

 immediatel}^ spread, forming the pilse ; they may enlarge and 

 remain distinct, or become absorbed and disappear upon alter- 

 nate pilge. The abdomen remains perfectly smooth for some 

 time after the lateral pilse are developed, not acquiring the 

 abdominal pilse until the third whorl is reached. Septa close 

 together and very intricate in the adult. Abdominal lobe broader 

 and deeper than the superior lateral. The inferior lateral is 

 nearly the same in size, and both are unequally divided into three 

 shallo-vt, minor lobes. Superior lateral cell lobiform and together 

 with the inferior lateral, unequally divided by two minor lobes. 



CosMOCERAS, Waagen, 180 9. 



Syn. — Parkinsonia, Bayle, 1818. 



Distr. — 42 sp. Jurassic. G. Galloviense, d'Orb. (xl, 46, 47). 



Siphonal side ( periphery) mostly with a smooth furrow ; sculp- 

 ture consisting mostly of dividing ribs, directed forwards at the 

 periphery, frequently ornamented with nodes or swellings ; mar- 

 gin of aperture in the young state frequently with ears, which 

 are lost by age ; body-chamber one-half whorl long. Lobes 

 moderately divided ; siphonal lobe distinctly shorter than the 

 first lateral ; second lateral repeating the form of the first ; one 

 or more auxiliaries. Aptychus apparently as in Stephanoceras. 



Perisphinctes, Waagen, 1860. 



Syn. — Ellipsolithes, Montf., 1808. Planulites, Montf., 1808. 

 Pictonia, Bayle, 1878. 



Distr. — 161 sp. Jurassic, Cretaceous. Perisphinctes arbiis- 

 tigerus, d'Orb. (xli, 60, 61). 



Shell mostly with wide umbilicus, with rounded external side, 

 sculpture consisting mostly of straight, undivided, not nodose 

 ribs; margin of aperture simple or with ears, with a constric- 

 tion ; also isolated constrictions on the inner whorls. Length of 

 body-chamber two-thirds to one whorl, mostly scarcely embracing 

 one circumference or turn. Lobular line similar to Stephano- 



