CRETACEOUS FORMATIONS. 5 



The neural plates are as narrow relatively as in the ordinary Chelones, and differ in 

 this respect from the broad rhomboidal plates in the Chelone Camperi of Maestricht. 

 The first and second are long and narrow, with almost parallel sides ; they are carinate 

 above, and the first is crossed by the indentation of the juncture between the first and 

 second vertebral scutes. The third and fifth are similarly indented. The eighth, 

 which is the smallest of the neural plates, is crossed near its anterior border, by the 

 impression of the juncture between the fourth and fifth vertebral scutes ; this neural 

 plate is 3 lines in length and 2 in breadth :* the ninth expands posteriorly into a 

 triangular form ; both these have their middle part raised into a ridge : the tenth 

 plate is suddenly expanded, with angular sides, which slope away from a median 

 longitudinal ridge : this is crossed by a transverse impression just anterior to its 

 junction with the pygal or median terminal plate ( P y) of the marginal series, which is 

 convex above and traversed by a median longitudinal furrow. The margins of this 

 plate meet posteriorly at an open angle. The second to the seventh pairs of costal 

 plates extend along the upper part of only the vertebral halves of the ribs, of which 

 they appear to be expansions. The length of such expanded part of the third rib 

 (pi. 3) is 9 lines ; its narrow, tooth-like part, before it reaches the marginal plate, is 

 9 lines ; about 3 lines of its extremity is inserted into the deep groove of the concave 

 surface of the sixth marginal plate, «6. The width of the interspace between the 

 narrow parts of the third and fourth ribs is 4 lines ; the length of the expanded part 

 of the first rib is 10 J lines ; the breadth of the expanded part of the first rib is 8 lines ; 

 the length of the narrow end of the rib, clear of the marginal plate, is 3 lines. In the 

 superior breadth of the first rib, the Chelone Benstedi agrees with existing turtles, and 

 differs strikingly from the Purbeck species. The last short rib {pi. 8) sends almost 

 directly backwards a short, narrow, tooth-like process, at right angles to the anterior 

 margin of its sub-triangular expanded part. In Chelone obovata it is extended more 

 nearly parallel with the expanded part. 



The marginal plates ( m 4 to py) have the same general uniformity of size which we 

 observe in the existing Chelones (see the Cuts 1 and 2, p. 3, of the ' Monograph on the 

 Reptiles of the London Clay') ; the posterior ones are not expanded as in the Purbeck 

 Chelone, and in certain Emydes, as Ernys serrata, &c. ; but the most decisive evidence 

 against the Emydian affinities of the present fossil is afforded by the form and develop- 

 ment of the inferior borders of the marginal plates attached to the fourth, fifth, and 

 sixth ribs (m7,m8, and m9, T. I, II, fig. 1) ; for these plates, instead of being expanded 

 and extended inwards to join the hyo- and hyposternals and to combine with these 

 elements of the plastron in forming the lateral supporting wall of the carapace, are 

 not so much developed in breadth as the same parts of the posterior marginal plates, 

 but form with them an even free border, as in other Chelones, in which not any of the 



* In all Emydes the proportions of this plate, "when it is not suppressed, are the reverse of those 

 in the fossil. 



