GREY CHALK MARL. 121 



Localities. Hamsey : very rare. 



37. Hamites armatus. Tab. xxiii. figs. 3, 4. Tab. xvi. fig. 5. 

 Depressed, ornamented with oblique annular costae, and four rows of 



tubercles, the marginal ones spinous ; siphunculus external ? Kmbs straight, 

 parallel. 



The characters of this beautiful Hamite were first developed by a gi- 

 gantic specimen found in a marl-pit at Koach, near Benson, in Oxfordshire, 

 by Professor Buckland, and figured in Min. Conch. ; previously to this 

 discovery, fig. 4 was the finest example extant. The casts of the shell 

 only remain, and the spinous processes are in consequence but rarely pre- 

 served. The form of the original was in aU probability cylindrical, but 

 the fossil specimens are in some degree flattened and distorted. The 

 limbs are straight, the hook or bend being very sudden. There are ge- 

 nerally one or two costae between each annular row of tubercles, and the 

 latter embrace two or three ribs. The spines are only known to proceed 

 from the two dorsal rows of tubercles ; but it seems probable, that the 

 other tubercles are also the rudiments of spinous processes, since all 

 of them are imperfect, and appear as if broken oiF. The septa are very 

 foliaceous. 



Tab. xvi. fig. 5, is a fine fragment from Hamsey; traces of the foMa- 

 ceous septa are visible at the fractured part. 



Tab. xxiii. fig. 3. View of one of the septa, or chambers, shewing its 

 foliaceous structure. 



fig. 4. This fine specimen has already been noticed ; it is 



so much distorted by compression, that only two rows of tubercles are 

 seen in this view : it was discovered at Hamsey by my brother. 



Locahties. Hamsey, Middleham : rare. 



38. Jlomite^ plicatilis. Tab. xxiii. figs. 1, 2. 



Subcylindrical, with numerous, oblique, annular ridges, and four rows 

 of spines : limbs curved. 



The curvature of the hmbs distinguishes this species from the one 

 above described, with which however, it closely corresponds in every other 

 particular. 



Tab. xxiii. fig. 1, is the only specimen yet discovered, in which the 



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