376 INFERIOR OOLITE AMMONITES. 
(Waagen).' | The former, however, is far less costate, and lacks the bullicostate 
character. The latter, by possessing this feature, is much closer; but it is much 
less umbilicate than the specimen before me. 
It is advisable to give further details in regard to the comparison of Sonn. 
densicostata and Sonn. polyacanthus, in order to prevent misunderstanding. In 
Sonn. densicostata the radius, minus carina, is 102 mm.; the umbilicus is 80 mm., 
and bullicoste begin at about 70 mm. radius. In Waagen’s figure, which is 
reduced one-half, at the radius 102— 2, the umbilicus is 33 x 2—66 mm., 
and knobs’ are plain at 16 x 2=32 mm. radius. Further, if what would have 
been the umbilicus of Sonn. densicostata at the same size as Waagen’s complete 
fossil be measured off—and this it is possible to do by following the inner curve 
(of the lost whorl) as indicated on the test,—the difference in umbilication is still 
more striking. Waagen’s own figures are (page 593 [87])—diameter 264 mm., 
umbilicus 114,mm.; whereas the umbilicus of densicostata at this diameter would 
have been 1835 mm. ‘This want of correspondence in umbilication is the most 
striking detail, but a comparison of densicostata and polyacanthus shows many 
other features of difference. 
This specimen of Sonn. densicostata is unique. It belongs to the Museum 
of Practical Geology, Jermyn Street, London; and my thanks are due to Mr. E. 
T. Newton, F.R.S., for obtaining the loan of it. Its horizon and locality are given 
as ‘‘ Inferior Oolite, Beaminster,” Dorset. The matrix suggests that it belongs to 
the Concavum-zone, though this surmise requires confirmation. Biologically, its 
affinities are with Sonn. polyacanthus ; but it is of an earlier type, as the later 
time of development of bullicostz indicates. The suture-line unfortunately is 
not shown; for the specimen is in too excellent condition, with well-preserved 
test complete. 
Sonninia soaupta, S. Buckman. Plate LXXXVII, figs. 1—3. 
Discoidal, compressed, carinate. Whorls ornamented at first with small 
regular spines, then for a space with small plain costz, to this succeeds a short 
length of alternate coste and spinicostz, which yields to small, closely-set, direct, 
nearly upright, plain cost, and these become larger and more distant later in life. 
3e série, t. xiii, pl. ii, 1884 (compare especially fig. 1) ; Haug, ““Amm. des Htages moyens,” ‘ Bull. 
Soc. géol. France,’ 3e série, t. xx, p. 308, 1893. 
1 « Zone Am. Sowerbyi,” ‘ Geogn.-pal. Beitrage,’ Band i, Heft 3, pl. xxix (vi), fig. 1, 1867. 
2 In Waagen’s figures the knobs are shown first as round pimples, later as more elongate. 
The shell, therefore, is first nodicostate, and later bullicostate. 
