AMMONITIDZ. 81 
side of the peripheral, two half-round ones limited partly by the 
preceding whorl. 8S. pseudo-anceps, Ebray. 
Canoceras, Hyatt, 1867. 
Distr.—C. centaurus, d’Orb. (xxxvi, 87, 88). Middle and 
Upper Lias. 
Pile on the periphery bifurcated ; lateral pile single or bifur- 
cated with one external row of tubercles, occurring regularly on 
each, or at intervals on widely separated pile. The young are 
very much flatter than the adults, and the sides consequently 
very narrow. They are smooth for the first one or two whorls, 
subsequently becoming tuberculated. The tubercles almost 
immediately spread, forming the pile; they may enlarge and 
remain distinct, or become absorbed and disappear upon alter- 
nate pile. The abdomen remains perfettly smooth for some 
time after the lateral pile are developed, not acquiring the 
abdominal pile 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 
shallow, minor lobes. Superior lateral cell lobiform and together 
with the inferior lateral, unequally divided by two minor lobes. 
CosMocERAS, Waagen, 1869. 
Syn.—Parkinsonia, Bayle, 1878. 
Distr.—42 sp. Jurassic. C. Calloviense, d’Orb. (xl, 46, 47). 
Siphonal side | periphery ) mostly with a smooth furrow ; sculp- 
ture consisting mostly of dividing ribs, directed forw ards at the 
periphery, frequently ornamented w ith 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.—Hllipsolithes, Montf., 1808. Planulites, Montf., 1808. 
Pictonia, Bayle, 1878. 
Distr.—161 sp. Jurassic, Cretaceous. Perisphinctes arbus- 
tigerus, Q’Orb. (xli, 60, 61). 
Shell mostly with wide umbilicus, with Younded 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- 
