ne Ammonites cordatus 
Sowerby, 1812. 
Original description 
(1813. — Sowerby, Min. Conch., Vol. I, PI. XVII, figs 2 and 4, p. 51-52). 
« AMMONITES cordatus. TAB. XVII. — Figures 2 and 4. 
« Spec. CHAR. Involute, rather depressed, carinated, inner turns half 
exposed ; surface with angular, projecting, undulating radii, extending over 
the inner half of each whorle, the remaining half covered by diverging 
undulations terminating in a crenated margin. Aperture cordate, two- 
fifths of the diameter of the shell long. Volutions four or five. 
« FROM one to two inches in diameter, and about one-third of its diameter in thickness; 
generally about five external undulations to two radii; no depression upon the edge. 
« The specimen, figure 2, shows the exterior surface of the [52] shell ; on it the radii are 
nearly equal in their thickness throughout, the external undulations are very prominent at 
their commencement, and the keel projects but little, hence the whole has a flatter aspect 
than No. 4. I gathered it myself in the better light coloured Limestone of Shotover in 
Oxfordshire, about the vear 1805. It is often found larger, but seldom so perfect. 
« No. 4 represents a cast of the interior, the radi terminate with an acute prominence, 
from which they sometimes branch into the external undulations, these are not so promi- 
nent as in No. 2. The margin or keel is also broader and thinner than that of No. 2, îts 
general contour is more uneven, and its sides appear more concave, [am much inclined to 
consider it as a distinct species. The specimen is a fine and instructive one, showing at the 
broad end the construction of the septa in an handsome manner, with the undulating and 
branching articulations which often give elegance to a specimen. This specimen is covered 
on the external part by an ochraceous Iron : the inside is light coloured Carbonate of Lime 
crystallized. It was sent me from Somersetshire by the late Mr. Cunnington. » 
OBSERVATIONS 
The holotype (fig. 2) is a small specimen, onlv one surface of which is exposed. It is 
evolute and somewhat compressed. The ribs are very straight until they pass from the side 
to the periphery, when they bend sharply forward. On the half-whorl which ends with the 
attainment of a diameter of 19mm, they are 12 in number : about the middle of the side ot 
the whorl they form tubercles and then bifurcate : on passing from the lateral to the peri- 
pheral area then show a tendency to build another row of tubercles. Only a small portion of 
the periphery is preserved but it is sufficient to show that the secondary ribs became finer 
and in one case bifurcation occurs, before they cross the keel, on which they form crenula- 
tions. At a diameter of 1gmm, the ratio of the width of the umbilicus to the diameter is 36. 
The paratype (fig. 4) is only a cast. The keel is sharp and the cross-section of the whorls 
is cordate. In the last whorl there are 15 strong, primary ribs, which after describing gentle 
\ double curves, form prominent tubercles about the middle of the side : from all but two ot 
these three secondary ribs arise, only two springing from each tubercle in the other cases. 
The secondary ribs sweep forward to the keel, on which they form crenulations, in a conti- 
nuous curve. Occasionally thev bifurcate before reaching the keel. At a diameter of 55mm, 
the ratio of the width of the umbilicus to the diameter is .29 and that of the thickness ofthe 
last whorl is .36. 
} Genus. — Cardioceras. Neumayr and Ublig, 1887. 
Horizon. — Fig. 2. Lower (?) Gorallian. Fig. 4. Upper Oxford Clay. 
hi: Locality. — Fig. 2. Shotover Hill, near Oxford. Fig. 4. Somersetshire. 
Remarks. — The difference between the photograph of the paratype and the original figure 
is striking, but there can be no doubt about its identity, as it bears a label on which is writ- 
ten in Sowerby’s handwriting (Ammonites cordatus M. C. 17, fig. 2, 4) and the green wafer 
with which he marked figured specimens. 
Both specimens are in the Sowerby collection in the British Museum. The date 1813 is 
given on the plate, but on the title page the date is 1812. 
EU 
1905. M. Healey. 
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