112 GREY CHALK MARL. 



This species differs from V. umhonata, in having the spire elevated 

 and the whorls inserted; the outer volution is not produced in any 

 specimens yet discovered. The line of separation between the wreaths, 

 is obscured by an extension of the substance of the shell, by which the 

 volutions are anchylosed, or cemented together. 



The specific name is in honour of James Sowerby, Esq. F.L.S. &c. 

 whose indefatigable exertions have very materially contributed to the 

 elucidation of the Natural History of the British Islands. 



Locality. Hamsey marl-pits. 



26. Serpula. 



A small group of serpulae have been discovered at Hamsey, by Mrs. 

 INIantell. I'he shell is smooth, and very tortuous, bearing some analogy 

 to S. glomerata ; but is probably a distinct species. 



27. Nautilus elegans. Tab. xx. fig. 1. tab. xxi. figs. 1. 4. 8. 

 Subglobose, umbilicate, transversely sulcated; sulci numerous, linear, 



curved, reflexed ; volutions one-third inserted ; septa concavo-convex, 

 entire ; siphunculus central ; aperture obtusely sagittate. 



The thickness of this nautilus is equal to twice its width. The sulci 

 are transverse, and very numerous, dividing the surface into broad, flat 

 costae ; these form an elegant curve on the back of the shell, and 

 proceeding laterally, are reflected towards the umbilicus. The septa are 

 gently undulated, and have their convex surface placed in an opposite 

 direction to that of the sulci, which they decussate. The siphunculus is 

 large and nearly central, and the umbihcus very small. In a young state 

 the sulci are wide, and separated by sharp transverse ribs, the whole sur- 

 face being marked by numerous longitudinal striee. 



Casts of this species are common in the grey marl of Sussex, and 

 Wiltshire, but no vestiges of the shell itself have been observed. The 

 pecimens are frequently oblique from compression, and seldom exhibit 

 the curved sulci in perfection ; they are from one to twelve inches in 

 diameter. 



Tab. XX. fig. 1. is a remarkably fine cast of an adult shell, in which 

 the sulci, with the broad and flat costae, the situation of the siphunculus, and 



