SIXTH, OR OXYNOTICERAN BRANCH. 219 
of this subseries. Quenstedt’s Amm. Guibahanus is not a true Greenoughi, and is 
properly referred by him to the radians group. An error is also shown by the 
use of this name for a species of the Middle Lias, since Guibalianus does not 
occur above the Lower Lias. 
The species as figured by Wright is a large shell, about 475 mm. in diameter, 
which has already lost the keel and pilw, the abdomen being rounded. The 
internal whorls of the original are heavily pilated, but the last whorl and a half 
are smooth. Sowerby’s figure is taken from a very large and aged specimen, and 
the pilations shown in the umbilicus indicate a shell with heavier folds at the same 
age than exist in either Hauer’s or Wright’s figures. Wright’s descriptions, how- 
ever, coincide with Sowerby’s figure, and the old of Sowerby’s shell has a com- 
pletely elliptical aged whorl. The size at which senility affects the shells, and 
the general characters and aspect of these figures, are the same as in Greenoughi. 
The young forms figured by Hauer may possibly be the young of this species; 
they seem to be too heavily pilated for the young of oxynotum. 
Oxynoticeras Guibali, Hyarr. 
Pl. X. Fig. 28, 29, 31. Summ. Pl. XIII. Fig. 14. 
Amm. victoris, Dum., Etudes Pal. Bass. du Rhone, II. p. 136, pl. xxxi., xlii. 
Amm, Guibali, Reyn¥s, Plates (pars). 
Amm. Guibalianus, Reynés, Ibid. 
Locality. — Lyme Regis? 
The keel of this species may begin to disappear in some specimens even at the 
size of 100 mm. In one specimen of the Semur collection this is accompanied by 
a singular and marked lateral deflection of the hollow keel, and at the size of 
170 to 180 mm. it had wholly disappeared, and the outer whorl had a very broad 
and gibbous abdomen; the sides, however, remained convergent and rounded. 
There is a specimen of this species from Lyme Regis in the Museum of Com- 
parative Zodlogy, which was found associated in the same slab with Cal. carusense 
and raricostatum. The diameter of this specimen is 145 mm. The keel is not 
present on the cast, as is usual in this species, but it had probably been present 
in the perfect shell, and evidently not impaired by age; the whorl and invo- 
lution of the sides were also not altered from the adult condition. A section 
showing the inner whorls had been formed by fracture, and the outlines of these, 
the hollow keel, and the amount of involution of the whorls, are the same as in 
Oxyn. Guibali. 
Amm. victoris, Dum., is evidently closely allied to Greenough, but, as figured 
by Dumortier, presents very peculiar sutures. It attains a large size before 
losing the keel, though one was seen by Dumortier which at a diameter of 
456 mm. had no keel. It may prove to be a form which is transitional between 
Greenough and this species. 
Ra aT 
SST SE ENCES RES 
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somernnainmion es 
