122 GREY CHALK MARL. 



spines remain ; they are composed of a thin peUicle of reddish brown sul- 

 phuret of iron, that has replaced the original shell. This example is part 

 of the lesser limb, broken off near the curvature ; it is inverted in the en- 

 graving. 



fig. 2, part of the larger Hmb, shewing traces of the folia- 



ceous septa. 



Localities. Hamsey, Middleham : very rare. 



S9. Hamites alternatus. Tab. xxiii. figs. 10, 11. 



Subcyhndrical, with oblique annular costse, and two rows of tubercles ; 

 tubercles marginal, placed on each alternate costa ; curvature gradual. 



I have seen but one fragment of this species, which, except in size, 

 agrees with H. spinulosiis of Sowerby, the tubercles being in all probability 

 the bases of spines ; it is however impossible to determine their identity 

 without more perfect examples. 



The specimen is elhptical from compression ; the ribs are very distinct 

 on the sides and back, but almost obliterated on the inner margin. The 

 tubercles are placed on each alternate rib, a circumstance that separates 

 this species from the other spiniferous hamites, previously described. 



Locality. Middleham. 



40. Hamites elUpticus. Tab. xxiii. fig. 9. 



Depressed, surrounded by even, undulating ridges, each ornamented 

 with two small tubercles placed on the outer margin ; curvature elliptical. 



This hamite appears to be identified by its even undulating ridges, 

 each furnished with two tubercles, and the elliptical form of its curvature. 

 It must however be acknowledged, that there is considerable difficulty in 

 distinguishing the essential characters of a fossil, from the variations that 

 are produced by age or accident, particularly when only a single specimen 

 is known. 



Locality. Middleham. 



41. Hamites attenuatus? Tab. xxiii. figs. 8. 13. 



This species has already been described as occurring in the Blue Marl. 

 (Vide Blue Marl Fossils, No. 21.) The specimens here figured are 

 nearly cylindrical, and covered with oblique annular striae ; it is however 

 doubtful whether they belong to the species referred to. 



