D. M. S. Watson—Chelonian from the Purbeck, Swanage. 311 
prevent the formation of red beds and perhaps also bleach the red 
marl immediately beneath the skerries. 
My thanks for criticism and suggestion are due to Mr. G. W. 
Lamplugh, and to Mr. EK, EK. L. Dixon whose knowledge of dolomitie 
rocks is both varied and extensive. 
EXPLANATION OF PLATE XXYVI. 
Fic. 1. Stone, 14 by 7 inches, in the east wall of south porch, Sutton-on- Trent 
Church, Notts. 
ee aroken and contorted alluvial silt in the left bank of the Prieska ravine 
where it opens on the Orange River. 
VI.— Giyerops rverimuerers (Lyp.), A CHELONIAN FROM THE Purbeck 
_ OF SwaNaGE. 
By D. M.S. Warson, B.Sc., the Victoria University of Manchester. 
‘{\HE Manchester Museum contains two ‘turtles’ from the Middle 
Purbeck Cap and Feather Bed of Swanage which are referable 
to Lydekker’s? Thalassemys ruetimeyert. The first of these, L. 7017, 
was purchased from Swanage in 1906, and consists of a carapace 
lacking all the marginals, but otherwise complete and undisturbed. 
The second, L. 9520, was obtained by the writer from a quarry some 
2 miles west of Swanage in March of this year. This specimen, 
although crushed, 1s important because it retains the whole shell, both 
carapace and plastron, with the exception of some of the peripherals. 
DEscRIPTION OF SPECIMENS. 
Carapace (Fig. 1).—The carapace is much depressed and is markedly 
cordiform. Its length from the anterior end of the nuchal to the 
posterior border of the last suprapygal is 28 cm., and the maximum 
width across the third costals is 26 em. The nuchal isa large hexagonal 
bone, the anterior edge of which is concave; its dimensions are— 
length 3 cm., breadth 6:8 cm. 
In. the two Manchester specimens two distinct bones lie between 
the inward ends of the first pair of costals; in Lydekker’s type- 
specimen, as is shown in his figure, and as Dr. Andrews has kindly 
checked for me, there is only one bone occupying the same space. 
The first of these bones is probably homologous with that which 
has been figured by Hay” and others in Chisternon, Boremys, 
Aspideretes, and Plastomenus as the preeneural; its condition in the 
present case is very similar to that which obtains in the last three 
genera. The neurals are generally hexagonal, with the face for the 
corresponding costal much larger than that for the preceding one. 
All eight are at present well developed. 
Two suprapygals are shown in L. 7017: the first isa hexagonal bone 
having a short border for the eighth neural and a long curved edge for 
the second suprapygal. The second suprapygal is quadrilateral and 
much wider in front. The costals gradually decrease in length from 
front to back; no pair meets in the middle line, and their form can be 
best understood from Text-fig. 1. 
1 R. Lydekker, Catalogue of the Fossil Reptilia in the British Musewm (Natural 
2): 1889, vol. il, p. 149. 
ORR: Hay, ‘The Fossil Turtles of North America” : Carnegie Institution, 
Publ. 75, 1908. 
