238 MOLLUSCA. CEPHALOPODA. OftiHOcEiiA. 
pers a little to the extremity, which is more obliquely placed than in the 
others, and produced into a blunt knob at the upper margin. The aperture 
is likewise a little contracted. 
b. Extinct species, 
* Surface of the shell smooth, 
1. O. lavis. — Shell conical, partitions waved ; chambers large ; syphon 
small and central. The length of the specimen which I possess is upwards 
of 3 inches. The breadth at the base is x®oths, and at the apex y%ths. The 
shell is very thin ; chambers about y%ths of an inch in depth ; partitions 
waved on both sides ; syphon in the middle of the shell about J^th of an inch 
wide. — O. superficie Isevi, Rutherglen, 306, t. xvi. f. 3. — O. Isevis, i^/m. 
Annals of Phil. v. 201, t. xxxi. f. 1.— In Carboniferous Limestme, 
2. O. pyramidalis. — Shell tapering, partitions slightly waved; chambers 
large, syphon small and central. This is longer in proportion to its breadth 
than the preceding ; the length of one specimen is upwards of 6 inches ; 1 inch 
and Y^ths at the larger end, and y^ths at the apex ; the last formed chambers 
are nearly y^o^hs of an inch in depth, while the oldest, towards the point, are 
scarcely y^th. A fragment found contiguous measured 2 inches in diameter. 
rn—Flem, An. Phil. v. p. 202, t. xxxi. f. 2. — In Carboniferous Limestone, 
3. O. cylindracea — Nearly cylindrical, partitions slightly waved, chambers 
numerous, pipe minute and central. In a specimen 3^th inches in length, 
y^ths at the base, and j^^th of an inch at the apex, the chambers are scarcely 
/gth in depth. When the shell is removed, the chambers appear very dis- 
tinct, with a flat surface — Flem. An. Phil. v. p. 202, t. xxxi. f. 3. — In Carbo~ 
niferms Limestone and Slate-clay of the coal-field. 
4. O. convexa ^Nearly cylindrical, partitions thin and concave ; syphon 
large and lateral. In a specimen inches long, the diameter at the base 
was l|th, and at the apex lower chambers are about ith of an 
inch in depth. The syphon is about ^^oths of an inch wide, and placed about 
midway between the centre and marg'in.— F/m. An. Phil. v. p. 202. t. xxxi, 
f.4. O.circularis, Smer, Min. Conch, t. 60. f. 6. 7* ? — In Carboniferous Limestone. 
5. O. attenuata. — Tapering, partitions nearly circular; chambers large. 
The shell of this species in one specimen is very thin, transparent, and glos- 
sy, and in some places is minutely striated across. Another specimen i®oths 
long, |th at the base, and 2gth at the apex, contains fifteen chambers. — In 
Slate-clay of the coal-field. 
6. O. Breynii — Conical, partitions waved on the syphon side ; the syphon 
itself is lateral, small, and cylindrical. — Maxtin^ Pet. Derb. t. 39, f. 4. Sower, 
Min. Conch, t. 60. f. 5. — Carboniferous Limestone. 
7. O. undulata Shell oval, thin, smooth ; partitions numerous, oblique, 
their edges rising, oval, with a wave on each side ; syphon lateral. — In Carbo- 
niferous Limestone. 
8. O. conica. — Shell long, conical, aperture oval ; chambers numerous ; sy- 
phon small, oval, nearly touching the margin. — Sower. Min. Conch, t.lx. f. 1, 
2, 3 In Lias. In the Geology of England and Wales, p. 268, this is con- 
sidered as the alveolus of a Belemnite. 
9. O. cordiformis . — “ Obconical ; base contracted ; sides convex ; aperture 
round septa numerous, placed directly across ; syphon not quite in the 
centre, the tube of which is inflated into a globular form between each sep- 
tum.— iS'ow^r. Min. Conch, t. ccxlvii — In Limestone of the Old Red Sand- 
stone, Closeburn, Dumfriesshire. 
2 
