CEPHALOPODA Ammonites Sowerbii 
(Miller, Mss.) J. Sowerby, 1821. 
Original description 
(1821. — Sowerby (James), Min. Conch., Vol. III, p. 23). 
« AMMONITES Sowerbii. TAB. CCXIIL. 
&« Sy. A. Sowerbii. Miller Mss. Catalogues. 
« Spec. CHar. Discoid, carinated, with about eight spiniform tubercles 
upon each whorl ; keel defined, entire ; aperture elliptical. 
« Var. B aperture circular, keel sometimes impressed. 
« Volutions about four, the inner ones concealed to the bases of the tubercles ; the outer 
part of the volutions has many gentle undulations; the inner part is even, except that the 
base of each tubercle is extended towards the centre in an obtuse ridge. The keel nearly 
separated from the body of the shell; it is round and entire. 
« In var. f the ridges from the bases of the tubercles are more prominent, and the keel 
sometimes so far sunk as to have a furrow on each side of it. The inner whorls of var. æ 
appear to be more gibbose than the outer ones. 
« Mr. Miller considers the shell figured as one of his rarest specimens : his collection has 
also to boast of several smaller specimens, belonging to var. B, which vary in the gibbosity 
of the whorls; they were all found at Dundry, in the Inferior Oolite. » 
OBSERVATIONS 
There are s whorls ; the inner ones rather obscured by matrix. The first seems to be 
smooth, and half the next irregularly spinous ; then, till the last whorl, spines are separated 
by, generally, two ribs (spinicostate and costate stage) ; on last whorl the interspinous costæ 
decline to striæ, the spines are prominent, each is connected by a costa to inner margin, and 
by 3 or 4 subcostæ to carina, in fact, numerous subcostæ occupy the whole ultra-spinous 
area (spinicostate and striisubcostate stage). About 7mm from the whorl, the spines may be 
seen preserved ; they are then incomplete : they were probably more than romm long. The 
inner whorls are gibbous, and presumably almost circular in section, the outer whorls less 
gibbous, and elliptical in section ; the peripheral area, beyond spines, is subconvexifastigate. 
The carina is prominent, conspicuously laterally sulcate ; so that its section is like the upper 
two thirds of the figure 8 ( « nearly separated from the body of the shell » — Sowerby) ; 
the carina is hollow (a septicarina), the infilling is conspicuously shewn where indicated by 
the arrow, and Sowerby in his section seems to have drawn this as the siphuncle. Of the 
suture-line only a part of the peripheral lobe can be seen. This indicates a suture-line fairly 
ornate, with somewhat long and narrow lobes and lobules. 
Genus. — Sonninia, Bayle. 
Locality and Horizon. — Inferior Oolite, Bajocian, zone of Ammonites Sauxei. The matrix 
attached to the specimen enables its exact position to be stated, namely the bed at Dundry 
known as the Ironshot (1896. — S. Buckman and E. Wilson, The upper portion of Dundry 
Hill ; Quart. Journ. Geol. Soc., Vol. LIT, p. 698, where the position of the species is given). 
Notes. — The var. (3, mentioned by Sowerby, would fit many species of Sonninia found 
at Dundry which are, in a biological sense, younger than À. Sowerbyi. The keel bordered by 
lateral furrows is a stage which precedes the keel laterally sulcate; and the more gibbous 
whorls precede the elliptical whorls. 
Mr. Miller notes how rare is the typical 4. Sowerbii. This agrees with the experience ot 
Mr. Wilson and myself in our researches at Dundry. There are several somewhat similar, 
elliptical whorled, spinous species, but they differ in proportions. From analogy with them, it 
may be suggested that À. Sowerbyi grows to a much larger size, and that the spines either 
fail completely at a larger diameter, or remain as papillæ, as in A». mesacanthus Waagen. 
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1904. S. S. Buchman. 
PALAEONTOLOGIA UNIVERSALIS. — 52% 
