RER OBOUA Ammonites vertebralis 
Sowerby, 1818. 
Original description 
(1818. — Sowerby, Min. Conch., Vol. II, p. 147, PI. CEXV). 
« AMMONITES vertebralis. TAB. CLXV. 
« Srec. CHar. Discoid. radiated, and carinated ; inner volutions partly 
concealed ; radii prominent, numerous, tuberculated in the middle, then 
furcate, with a tubercle upon each branch ; carina serrato-tuberculate ; 
aperture orbicular. 
« À vERY handsome shell whose radii are a little undulated, and together with the tuber- 
cles upon them, are sharpish and compressed ; they are very regularly furcate, and each 
branch has a tubercle about its middle, then passes on in an elegant curve to the carina, 
where it forms another somewhat reflected tubercle—the two branches again unite on the 
other side. The thickness is about equal to one-third of the diameter. 
« The Rev. W. Buckland has enabled me to exhibit this with his usual fondness for 
science; he informs me that it is found at Dry Sandford and Marcham, two adjoining vil- 
lages on the N. W. of Abingdon, Berkshire, where it lies in silicious sandy beds, that 
contain subordinate Strata of a gritty Limestone, composed of small Quartz pebbles, sand, 
and shelly fragments, united by a calcareous cement. 
« I have not seen the outside of the shell, but from the space between the whorls in the 
cast, I suppose it must-have been thick. It is named vertebralis from the resemblance of the 
carina to the vertebral processes in some quadrupeds. » 
OBSERVATIONS 
Only the cast is preserved. The cross-section of the whorl is squarish and the involution 
amounts to about 1/3. On the whorl which ends with the attainment of a diameter of 
gomm, there are 24 primary ribs : they run backwards on the wall of the umbilicus. but on 
reaching the side of the whorl they bend forwards and continue radially : in the middle of 
the side they form prominent, somewhat longitudinally compressed tubercles, after which 
all but two bifurcate : the secondary ribs so formed, bend forwards on reaching the peri- 
phery and meeting those of the opposite side in the median line, help to form the somewhat 
coarse, knotted keel, which suggested the specific name to Sowerby. The prominence of the 
ribs at the junction of the lateral and peripheral areas indicate that there would have been 
another row of tubercles here, had the test been preserved. The body-chamber occupies 3/4 
of the last whorl. The ratio of the width of the umbilicus to the diameter, when the latter 
is gomm, is .34, and that of the thickness of the last whorl to the diameter is .41. 
Genus. — Cardioceras Neumayr und Uhlig, 1881. 
Horizon. — In the Supplementary Index, p. 249, this species is referred to the Portland 
Rock. Its true horizon is Lower Corallian (Lower calcareous Grit). 
Locality. — Marcham, 2 !/ miles W. of Abingdon, in Berkshire. 
Remarks. — This type is in the Buckland collection in the University Museum Oxford. It 
bears no label stating that it is a specimen figured by Sowerby, but that it is the original 
specimen cannot be doubted. Two figures of it are given, the lower being an oblique view, 
showing the keel. 
Sowerby states, rather vaguely, that the type is found at Dry Sandford and Marcham, but 
Buckland has written the word « Marcham » on it. 
1905. M. Healey. 
PALAEONTOLOGIA UNIVERSALIS. — 93? 
