238 MOLLUSCA. CEPHALOPODA. Okthocera. 



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. Icevis — 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 T 9 5 ths, and at the apex y^ths. The 

 shell is very thin ; chambers about T 2 5 ths of an inch in depth ; partitions 

 waved on both sides ; syphon in the middle of the shell about J 5 th of an inch 



wide.— O. superficie laevi, lire's Rutherglen, 30G, t. xvi. f. 3 O. Ivevis, Flem. 



Annals of Phil. v. 201, t. xxxi. f. 1. — In Carboniferous Limestone. 



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 indies ; 1 inch 

 and T 2 5 ths at the larger end, and T 2 5 ths at the apex ; the last formed chambers 

 are nearly t 3 5 ths of an inch in depth, while the oldest, towards the point, are 

 scarcely T ' 3 th. A fragment found contiguous measured 2 inches in diameter. 

 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, 

 T 4 5 ths at the base, and , 3 th of an inch at the apex, the chambers are scarcely 

 , l 5 th 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- 

 niferous Limestone and Slate-clay of the coal-field. 



4. O. convexa Nearly cylindrical, partitions thin and concave ; syphon 



large and lateral. In a specimen 4J inches long, the diameter at the base 

 was l£th, and at the apex , 8 n ths. The lower chambers are about itfi of an 

 inch in depth. The syphon is about i 3 ths of an inch wide, and placed about 

 midway between the centre and margin — Flem. An. Phil. v. p. 202. t. xxxi. 

 f.4. O. circularis, Sower. Min. Conch, t. 60. f. 0. 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 ^ths 



long, |th at the base, and j'gth at the apex, contains fifteen chambers In 



Slate-clay of the coal-field. 



G. O. Breynii — Conical, partitions waved on the syphon side ; the syphon 

 itself is lateral, small, and cylindrical. — Martin, Pet. Derb. t. 39, f. 4. Sower. 

 Min. Conch, t. 00. 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. 208, 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. — Sower. Min. Conch, t. ccxlvii — In Limestone of the Old Red Sand- 

 stone, Closeburn, Dumfriesshire. 



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