ACICHELYID^. 149 



Wiltshir . This specimen agrees precisely with the fourth 

 costal of the type shell figured by Riitimeyer in the ' N. 

 Denkschr. schw. Ges. Nat.' vol. xxv. art. 2, pi. i. 5 the 

 antero-posterior diameter of this specimen and of the cor- 

 responding costal of the type being 0,064 (2*5 inches). 

 Irrespective of its larger dimensions, this specimen is at 

 once distinguished from Tropidemys by the unequal size 

 of the facets for the neurals. The smoothness of the shell 

 distinguishes the specimen from most species of Plesio- 

 chelys, while the peculiar point running down between 

 the 5th neural and oth costal is a feature found only in 

 the present form. These specimens are specifically the 

 same as the preceding. 



Gunnington Collection. Purchased, 1875. 



47327. Several fragments of shell, apparently associated with the 

 preceding, some of which seem to belong to the plastron : 

 from Devizes. Cunnington Collection. 



46328. A right femur ; from the Kimeridge Clay of Devizes. This 

 specimen was probably associated with the above-men- 

 tioned fragments of the shell obtained from the same 

 locality. It resembles the smaller femur of No. R. 1645. 

 Its length is 0,166 (6*5 inches). Cunnington Collection. 



Thalassemys ruetimeyeri, Lydekker, n. sp. 



Carapace deeply emarginate anteriorly, with the 2nd, 3rd, and 

 4th vertebral shields widest in front; neurals shorter and wider 

 than in the type species. Size unknown. 



Hah. Europe (England). 



40676. Slab showing the dorsal aspect of the nearly entire carapace 

 (Fig.) of an immature individual ; from the Purbeck of Swanage, 

 Dorsetshire. The type specimen (fig. 36). Noticed by G. 

 A. Boulenger and the present writer in the ' Geol. Mag/ 

 dec. iii. vol. iv. p. 274, and provisionally referred to 

 Acichelys (Eury sternum). With the exception of the first 

 marginal of either side and the second of the left side, 

 the whole of the peripheral bones are wanting, and the 

 second, third, and fourth neurals are likewise missing. 

 The contour of the vertebral shields is distinctly defined. 

 In their narrowness these shields differ very markedly 

 from those of immature specimens of Acichelys. The 

 costals are ossified nearly up to the extremities of the 

 ribs. Pur chased. 1867. 



