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PROM

 THE 
 WEALBEN 
 AND 
 TURBECK. 
 513 
 

one

 may 
 be 
 named 
 interpectoral. 
 On 
 this 
 view 
 the 
 gnlars 
 will 
 

have

 been 
 placed 
 anteriorly 
 to 
 the 
 intergular 
 in 
 the 
 same 
 manner 
 

as

 in 
 Chelodina. 
 

Our

 specimens 
 indicate, 
 therefore, 
 a 
 Chelonian 
 of 
 medium 
 size, 
 

characterized

 by 
 the 
 occurrence 
 of 
 a 
 row 
 of 
 median, 
 and 
 probably 
 

azygos,

 plastral 
 shields, 
 dividing 
 the 
 normal 
 plastral 
 shields 
 below 
 

the

 gulars. 
 This 
 series 
 is 
 a 
 continuation 
 of 
 the 
 intergular 
 now 
 

found

 in 
 all 
 Pleurodira 
 and 
 some 
 Cryptodira, 
 and 
 may 
 in 
 all 
 proba- 
 

bility

 be 
 regarded 
 as 
 indicating 
 an 
 archaic 
 type 
 of 
 structure, 
 the 
 

Chelonian

 plastron 
 having 
 probably 
 been 
 developed 
 from 
 abdominal 
 

ribs

 like 
 those 
 of 
 SpJienodon, 
 and 
 apparently 
 showing 
 a 
 tendency 
 to 
 

the

 obliteration 
 of 
 some 
 of 
 its 
 elements 
 with 
 advancing 
 specializa- 
 

tion.

 No 
 existing 
 Chelonian 
 exhibits 
 this 
 multiplication 
 of 
 plastral 
 

shields

 ; 
 but 
 Mr. 
 Boulenger 
 has 
 figured 
 a 
 minute 
 interanai 
 shield 
 

in

 two 
 specimens 
 of 
 Macroclemmys, 
 one 
 of 
 which 
 also 
 exhibits 
 an 
 

equally

 minute 
 azygos 
 shield 
 in 
 the 
 centre 
 of 
 the 
 plastron. 
 

A

 feature 
 of 
 a 
 somewhat 
 analogous 
 nature 
 to 
 that 
 characterizing 
 

the

 plastron 
 under 
 consideration 
 is, 
 however, 
 found 
 in 
 the 
 carapace 
 

of

 a 
 Chelonian 
 from 
 the 
 Kimeridgian 
 of 
 Hanover, 
 figured 
 by 
 Dr. 
 

Portis

 in 
 the 
 ' 
 Palseontographica,' 
 vol. 
 xxv. 
 pi. 
 xv., 
 under 
 the 
 name 
 

of

 Trojpidemys 
 Seebachi. 
 In 
 that 
 specimen 
 the 
 normal 
 azygous 
 series 
 

of

 vertebral 
 shields 
 is 
 divided 
 into 
 two 
 lateral 
 series 
 by 
 a 
 more 
 

numerous

 row 
 of 
 small 
 intervertebral 
 shields, 
 nearly 
 corresponding 
 

in

 number 
 with 
 the 
 underlying 
 neural 
 bones. 
 In 
 the 
 characters 
 of 
 

the

 bony 
 elements 
 of 
 the 
 carapace 
 that 
 specimen 
 corresponds 
 closely 
 

with

 typical 
 species 
 of 
 Tropideinys 
 • 
 but 
 the 
 multiplication 
 of 
 the 
 

shields

 should 
 not 
 improbably 
 be 
 regarded 
 as 
 a 
 generic 
 character. 
 

It

 occurs 
 to 
 me 
 that 
 the 
 carapace 
 of 
 the 
 Wealden 
 form 
 may 
 perhaps 
 

have

 had 
 a 
 similar 
 series 
 of 
 intervertebral 
 shields. 
 

b.

 The 
 Affinities 
 of 
 Pleurosternum. 
 

The

 Purbeck 
 Chelonian 
 to 
 which. 
 Sir 
 R. 
 Owen 
 applied 
 the 
 name 
 

Pleurosternum

 latiscutatum, 
 as 
 has 
 been 
 shown 
 by 
 Mr. 
 Poulenger 
 and 
 

myself,

 has 
 no 
 connexion 
 with 
 the 
 Pleurosternidse 
 *, 
 but 
 belongs 
 to 
 

the

 Plesiochelyidse 
 ; 
 and 
 from 
 the 
 evidence 
 afforded 
 by 
 a 
 nearly 
 entire 
 

shell

 of 
 the 
 last-named 
 species 
 from 
 the 
 Wealden, 
 it 
 appears 
 that 
 

the

 plastra 
 described 
 by 
 Sir 
 E. 
 Owen 
 as 
 Platemys 
 Mantelli 
 and 
 

P.

 Dixoni 
 are 
 really 
 referable 
 to 
 the 
 so-called 
 Chelone 
 Belli, 
 which 
 

is

 thus 
 shown 
 to 
 be 
 an 
 allied 
 form. 
 

It

 may 
 also 
 be 
 observed 
 in 
 this 
 connexion 
 that 
 the 
 so-called 
 

Pleurosternum

 latiscutatum 
 was 
 provisionally 
 referred 
 by 
 my 
 friend 
 

and

 myself 
 in 
 the 
 paper 
 above 
 cited 
 to 
 the 
 genus 
 Plesioclielys. 
 Subse- 
 

quent

 observations 
 have, 
 however, 
 shown 
 that 
 the 
 vertebral 
 shields 
 

are

 much 
 wider 
 than 
 in 
 that 
 genus 
 ; 
 and 
 since 
 there 
 are 
 other 
 

distinctive

 features 
 which 
 I 
 shall 
 indicate 
 elsewhere, 
 I 
 feel 
 jus- 
 

tified

 in 
 proposing 
 the 
 new 
 generic 
 name 
 Hylaioclielys 
 for 
 this 
 

Chelonian.

 I 
 may 
 state, 
 however, 
 that 
 I 
 have 
 found 
 it 
 impossible 
 

 G-eol. 
 Mag. 
 decade 
 3, 
 vol. 
 iv. 
 p. 
 272 
 (1887). 
 In 
 this 
 communication 
 

Pleurosternum

 was 
 referred 
 to 
 the 
 Pelomedusidae. 
 

Q.

 J. 
 G. 
 S. 
 No. 
 179.