GENUS XIX. NAUTILUS. 93 



formed by transverse partitions ; imperforate (see Park. 

 Organ. Rem. 3. p. 14S. t. 10. f. 13 to 37). 



Hpirula. Shell partially or completely spiral and wheel- 

 shaped ; the whorls separated ; the last whorl especially 

 elongated in a right line ; the transverse partitions sim- 

 ple, and pierced by a tube ; the aperture circular (see 

 N. Spirula, f. 55). 



TuRRiLiTES. Shell spiral and turbinated ; the whorls con- 

 tiguous and all apparent ; the internal part joined by 

 sinuous sutures ; the transverse partitions lobed and 

 pierced ; the aperture round (see Park. Organ. Rem. 3. 

 p. 146. t. 10. f. 12). 



Baculites. Sliell straight, cylindrical, and rather conical, 

 divided into chambers by transverse, sinuous, and imper- 

 forate partitions ; the sutures indented like the battlements 

 of a tower (see Park. Organ. Rem. 3. p. 1 42. t. 9. f. 2). 



Ortiiocera. Shell straight or arched, rather conical ; the 

 chambers distinct, formed by transverse simple partitions, 

 perforated by a central or lateral tube (see N. Fascia, 

 f. 57, and Park. Organ. Rem. 3. p. 111. t. 7. f. 14). 



HiPPURiTES. Shell conical, straight, or arched, furnished in- 

 ternally with transverse partitions, and with two longi- 

 tudinal, lateral, obtuse and converging ridges ; the last 

 chamber closed by an operculum (see Park. Organ. 

 Rem. 3. p. 1 1 S. t. 8. f. 1 and 5). 



Belemnites. Shell straight, like a long cone, pointed, full 

 at the summit, and furnished with a lateral gutter ; only 



