﻿KIMMERIDGE CLAY. 



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neurapophysis extends forward to form the prezygapophysis (ib., and PL XII, fig. 1, ~). 

 The ridge (<?), rising to the costal pit, forms or extends its hind border and is thence 

 continued, expanding or thickening, into the ridge which forms the diapophysial buttress,/. 

 The ridge (PI. XIII, fig. 3, a ) does not, in this vertebra, combine with the ridge, e, to form 

 the buttress, as in the lguanodon (Mon. cit. Tab. VII, fig. 2), but appears as a shorter 

 independent ridge. A median ridge (PI. XII, fig. 1, r) rises from above the interspace 

 of the prezygapophyses to the neural spine, n s. Another median ridge (PL XIII, fig. 1, s) 

 extends along the back of the neural arch and rises to the interspace of the postzygapo- 

 physes, s, /. The chief expanse of the summit of the neural arch in the antero- 

 posterior direction is a zygapophysial one (PI. XIII, fig. 2, z, z ') ; in the transverse 

 direction it is a diapophysial expansion (ib., fig. 1, d, d). 



Each diapophysis is three-sided ; the broadest facet is on the upper side, forming 

 with the zygapophyses the neural platform. External to the zygapophyses this surface 

 is 2^ inches from before backward ; it is flat. The postinferior surface (PL XIII, 

 fig. 1, /, d) is in that direction concave, most so below the postzygapophyses, z ', and 

 growing shallower to the tumid extremity, d, of the transverse process. The least 

 fore-and-aft diameter of this surface of the diapophysis is 2 inches 3 lines, that of the 

 anteroinferior surface is 1 inch 5 lines ; this is feebly concave across, and is divided 

 lengthwise for part of its extent by the zygapophysial ridge (PL XII, fig. 1, t)- 



The free end of the diapophysis is swollen and tuberous ; a well-marked facet 

 (PL XII, fig. 1, d, and PL XIII, fig. 2, d) cuts the lower part obliquely j it is of a 

 rhomboid shape, nearly flat, and is roughened for the ligamentous attachment of the 

 ' tubercle of the rib y it measures 2\ inches by 1 inch 9 lines. 



The postzygapophyses (PL XIII, fig. 1, /) are formed by an expansion backward 

 of the neural platform, the. pair of processes being indicated by a medial notch; they 

 are more clearly defined by their flat articular surfaces, which are subtriangular in shape, 

 the angles being rounded off ; their longest diameter is 2 inches : they look outward and 

 downward. 



The prezygapophyses (PL XII, fig. 1, ~, c) have been mutilated in the present vertebra, 

 but the extent of their basal origin, 2 inches, may be traced ; they are more distinct 

 productions of the neural platform, which abruptly sinks to the level of their medial 

 borders. 



The anterior basal ridge (ib., ?•) of the neural spine begins at this lower part of the 

 platform, which it divides into a pair of hollows. The spine rises freely from the 

 broader upper level of the platform. Its base here has a fore-and-aft extent of 3 inches 

 8 lines. The hind border of the spine is rather sharp ; the thickest part of the body of 

 the spine is 9 lines ; its free termination was probably, from the analogy of a caudal 

 vertebra subsequently to be described, swollen and tuberous. 



A vertebral centrum and a portion of the neural arch, from the same region of the 

 spinal column, repeat the characters, so far as they are shown, of the less fragmentary 



