234 ADDENDA. 



R. 1673. Slab of rock exhibiting the ventral aspect of the imperfect 

 hinder portion of the right side of the plastron, together 

 with portions of two costal bones, the head of a femur, 

 and the centrum of a caudal vertebra, of a large Che- 

 Ionian probably referable to this form ; from the Portland 

 Oolite of the Isle of Portland. The plastron exhibits 

 portions of the hyo-, hypo-, and xiphiplastrals, with the 

 sulci of the overlying shields ; and there is a large mesial 

 vacuity. There appears to have been no mesoplastral, 

 and in the shortness and width of the hypoplastral the 

 specimen agrees very closely with the Acichelyidce 1 , and 

 differs from the Plesiochelyidce. Allowing for the effects 

 of crush, the femur appears to agree closely in size with 

 that of Thalassemys, No. E. 1645 (p. 148). 



Presented by G. Clifton, Esq., 1889. 



Geneeicallt Undetekmined Specimens. 



a. From the London Clay. 



49981. The imperfect proximal extremity of the left humerus of a 

 Chelonian of the approximate size of a small individual 

 of Podocnemis eccpcmsa ; from the London Clay of the 

 Isle of Sheppey. This specimen closely resembles the 

 humerus of existing Pleurodirans, and probably belongs 

 to that section. Wetherell Collection. Purchased, 1871. 



b. From the Chalk. 



49924. Fragment of chalk, showing the dorsal aspect of a left 

 coracoid ; from the Lower Chalk of Glynde, near Lewes, 

 Sussex. In its extremely expanded form this specimen 

 resembles the coracoid of Chelys, and is unlike that of 

 most of the Chelonidce 2 . It is nearly of the same size 

 as the coracoid of Chelys, and would agree approximately 

 in relative' size with the mandible (No. 49220) mentioned 

 on p. 181, with which it may perhaps have been asso- 

 ciated. C 'apron Collection. Purchased, 1879. 



1 Compare Eaitimeyer, N. Denkschr. sckw. Ges. Nat. vol. xxv. art 2, pi. xvii. 

 j.l. 



2 Lytoloma crassicostahcm comes nearest in this respect. 



