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56

 MB. 
 B. 
 LYDEKKEE 
 ON 
 THE 
 BEMAUT6 
 ABB 
 AFFINITIES 
 

This

 genus 
 forms 
 a 
 link 
 connecting 
 other 
 forms 
 with 
 Pliosau 
 r 
 rus 
 r 
 

and

 will 
 be 
 characterized 
 by 
 its 
 comparatively 
 short 
 neck, 
 large 
 

head

 and 
 carinated 
 teeth, 
 elongated 
 mandibular 
 symphysis, 
 short 
 

cervical

 vertebrae, 
 having 
 donble 
 costal 
 facets 
 and 
 flattened 
 terminal 
 

faces,

 with 
 complete 
 anchylosis, 
 in 
 the 
 adult, 
 of 
 the 
 arches 
 and 
 ribs 
 

with

 the 
 centra. 
 In 
 the 
 pectoral 
 girdle 
 there 
 is 
 a 
 small 
 omo- 
 

sternum

 ; 
 the 
 scapulas 
 have 
 a 
 flattened 
 and 
 large 
 ventral 
 surface, 
 

the

 dorsal 
 portion 
 being 
 smaller 
 than 
 in 
 TJiaumatosaurus 
 ; 
 and 
 the 
 

eoracoids

 have 
 no 
 distinct 
 median 
 production 
 in 
 advance 
 of 
 the 
 line 
 

of

 the 
 glenoid 
 cavity. 
 In 
 the 
 limbs 
 the 
 epipodials 
 are 
 less 
 elongated 
 

than

 in 
 the 
 last-named 
 genus. 
 Finally, 
 Pliosaurus 
 itself 
 is 
 dis- 
 

tinguished

 by 
 its 
 still 
 larger 
 head 
 and 
 teeth 
 ; 
 the 
 still 
 shorter 
 neck 
 r 
 

in

 which 
 the 
 vertebrae 
 are 
 less 
 elongated 
 and 
 more 
 flattened, 
 the 
 

costal

 facets 
 are 
 more 
 distinctly 
 double, 
 and 
 the 
 arches 
 and 
 ribs 
 unite 
 

merely

 by 
 synchondrosis 
 with 
 the 
 centra. 
 The 
 pectoral 
 girdle 
 is 
 of 
 

the

 same 
 general 
 type 
 ; 
 but 
 the 
 omosternum 
 may 
 have 
 been 
 totally 
 lost. 
 

Both

 genera 
 have 
 similarly 
 elongated 
 ischia 
 : 
 but 
 the 
 epipodials 
 of 
 

Pliosaurus

 have 
 become 
 so 
 shortened 
 as 
 to 
 lose 
 all 
 resemblance 
 to 
 

"

 long 
 bones."' 
 

With

 the 
 evidence 
 of 
 Peloneustes 
 before 
 us 
 we 
 now 
 have 
 an 
 

almost

 continuous 
 chain 
 connecting 
 the 
 genus 
 Plesiosaurus 
 with 
 

Pliosaurus,

 the 
 course 
 of 
 evolution 
 being 
 directed 
 towards 
 a 
 gradual 
 

increase

 in 
 the 
 size 
 of 
 the 
 head, 
 in 
 the 
 length 
 of 
 the 
 mandibular 
 

symphysis,

 and 
 the 
 size 
 and 
 specialization 
 of 
 the 
 teeth, 
 accompanied 
 

by

 a 
 shortening 
 of 
 the 
 neck, 
 which 
 is 
 accomplished 
 by 
 a 
 reduction 
 

both

 in 
 the 
 number 
 and 
 length 
 of 
 the 
 component 
 vertebras, 
 and 
 also 
 

by

 a 
 tendency 
 to 
 a 
 loose 
 attachment 
 between 
 the 
 centra, 
 arches, 
 

and

 cervical 
 ribs 
 of 
 the 
 vertebras, 
 and 
 a 
 reduction 
 in 
 the 
 relative 
 

length

 of 
 the 
 epipodial 
 bones 
 of 
 the 
 limbs. 
 That 
 Peloneustes 
 phUar- 
 

chus

 is 
 the 
 direct 
 ancestor 
 of 
 Pliosaurus 
 is, 
 however, 
 improbable, 
 see- 
 

ing

 that 
 the 
 latter 
 genus 
 is 
 already 
 represented 
 in 
 the 
 Oxford 
 Clay. 
 

Finally,

 while 
 Pliosaurus 
 forms 
 the 
 culmination 
 of 
 the 
 series 
 just 
 

indicated,

 the 
 genus 
 Polyptychodon 
 appears 
 to 
 have 
 been 
 the 
 latest 
 

development

 of 
 the 
 series 
 of 
 which 
 the 
 middle 
 term 
 is 
 represented 
 

bv

 Cimoliosaurus. 
 

Y.

 The 
 Aeeixities 
 or 
 G-eosaeees. 
 

In

 a 
 recent 
 number 
 of 
 the 
 ' 
 Geological 
 ILagazine 
 ' 
 * 
 I 
 have 
 shown 
 

that

 the 
 genus 
 Geosaurus, 
 from 
 the 
 Lower 
 Ximeridgian 
 of 
 Bavaria, 
 

is

 undoubtedly 
 a 
 Crocodilian 
 allied 
 to 
 3Ietrior7ii/iichus 
 ; 
 and 
 a 
 

skeleton

 of 
 the 
 latter 
 genus 
 from 
 the 
 Oxford 
 Clay 
 near 
 Peterbo- 
 

rough,

 lately 
 sent 
 by 
 lEr. 
 A. 
 X. 
 Leeds 
 to 
 the 
 Xatural 
 History 
 

Aiuseuru,

 has 
 enabled 
 me 
 to 
 make 
 a 
 closer 
 comparison 
 between 
 the 
 

two,

 of 
 which 
 a 
 summary 
 is 
 now 
 given. 
 First, 
 it 
 appears 
 from 
 

several

 skeletons 
 in 
 the 
 collection 
 of 
 ILr. 
 Leeds, 
 as 
 well 
 as 
 from 
 the 
 

type

 of 
 Geosaurus, 
 that 
 these 
 Crocodiles 
 have 
 no 
 dermal 
 scutes, 
 but 
 

that

 bony 
 plates 
 were 
 developed 
 in 
 the 
 sclerotic 
 of 
 the 
 eye. 
 The 
 

 Decade 
 iii. 
 vol. 
 v. 
 p. 
 452