File:The Quarterly journal of the Geological Society of London (13937061631).jpg

234

ItlR.

 E. 
 LYDEKKER 
 ON 
 REMAINS 
 OF 
 EOCENE 
 AND 
 MESOZOIC 
 

that

 the 
 shell 
 alone 
 is 
 insufficient 
 to 
 afford 
 certain 
 generic 
 characters. 
 

For

 the 
 same 
 reason 
 the 
 term 
 Propleura 
 of 
 Cope 
 (1870) 
 must 
 be 
 re- 
 

jected.

 We 
 have, 
 however, 
 the 
 name 
 Lytoloma, 
 Cope, 
 based 
 on 
 the 
 

evidence

 of 
 the 
 mandible, 
 and 
 which 
 is 
 earlier 
 than 
 Glossoohdys, 
 

Seeley

 (1871), 
 which 
 was 
 based 
 on 
 the 
 skull. 
 There 
 is, 
 indeed, 
 the 
 

name

 Puppigerus, 
 Cope 
 (1870). 
 The 
 type 
 of 
 that 
 genus 
 must 
 be 
 

taken

 to 
 be 
 Chelone 
 longiceps, 
 Owen, 
 as 
 being 
 the 
 first-mentioned 
 of 
 

Fig.

 2. 
 — 
 Ventral 
 and 
 Lateral 
 Aspects 
 of 
 the 
 Imperfect 
 Mandible 
 of 
 

Lytoloma

 cantabrigiense 
 ; 
 from 
 the 
 Cambridge 
 Greensand. 
 

(Nat.

 size.) 
 

the

 English 
 Eocene 
 forms 
 on 
 which 
 that 
 genus 
 is 
 based. 
 Now 
 the 
 

skull

 of 
 that 
 form, 
 as 
 I 
 have 
 recently 
 found, 
 is 
 similar 
 to 
 that 
 of 
 the 
 

young

 of 
 the 
 so-called 
 Chelone 
 crassicostata, 
 one 
 of 
 the 
 typical 
 forms 
 

of

 Euclastes 
 ; 
 and 
 Puppigerus 
 is 
 therefore 
 a 
 synonym 
 of 
 the 
 latter. 
 

The

 names 
 Lytoloma 
 and 
 Puppigerus 
 occur 
 in 
 the 
 same 
 volume 
 ; 
 but 
 

since

 the 
 former 
 comes 
 first, 
 and 
 the 
 latter 
 includes 
 forms 
 which 
 

are

 distinct, 
 I 
 propose 
 to 
 adopt 
 Lytoloma 
 in 
 the 
 place 
 of 
 Euclastes. 
 

I

 may 
 also 
 mention 
 that 
 in 
 young 
 individuals, 
 and 
 perhaps 
 in 
 the 
 

adult

 of 
 some 
 of 
 the 
 apparently 
 smaller 
 forms, 
 like 
 L. 
 trigoniceps 
 of 
 

the

 Bracklesham 
 beds, 
 the 
 mandibular 
 symphysis 
 (as 
 shown 
 by 
 a 
 

specimen

 in 
 the 
 Museum 
 of 
 Practical 
 Geology) 
 is 
 shorter 
 and 
 more 
 

convex

 than 
 in 
 the 
 adult 
 of 
 L. 
 crassicostatum 
 and 
 L. 
 planimentum, 
 and 
 

is

 thus 
 almost 
 similar 
 to 
 the 
 mandible 
 of 
 Thalassochelys. 
 

In

 these 
 respects 
 the 
 present 
 mandible 
 agrees 
 very 
 closely