Alfred Harker—On some Anglesey Dykes (No. IIL.) 267 
2. How have the proccelous caudal vertebra of the Propleuride 
become the opisthoccelous caudal vertebra of the Chelydride? Could 
they have turned themselves the other way? How could the nuchal 
rib, lost by the Propleuride,! be present in their descendants, the 
Chelydrida ? 
3. Whichever might have been the origin of the Chelonide,’ their 
relations with the Propleuride do not seem to allow of a diphyletic 
phylogenetic tree for. these two families. 
XI.—Therefore, we should more likely have: 
Chelonide. 
Propleuride. 
Trionychide. Chelydride. 
so. _————————— —— 
DACTYLOPLASTRINE CRYPTODIRAN T'HECOPHORIAN CHELONIANS. 
XIJ.—One more word before concluding. The Propleuride not 
being true Turtles, were they pelagic in their habits? The marine 
nature*® of the deposit proves nothing in this case, the beds in 
question containing also Trionyxz, which, as is well known, lives in 
rivers. 
The humerus of the Propleuwride has already shown us that the 
limbs of these Chelonians were less well adapted to aquatic life than 
those of the true Turtles, but that they were more so than those of 
Chelydra, or even than those of Trionyx. The metapodials point also 
in the same direction. As is equally demonstrated by the carapace 
and diet,* Huclastes was, therefore, probably a very littoral marine 
type. 
VI.—Woopwarpi1an Musrum Norrs: on sommz ANGLESEY DYKES. 
‘ No. III. 
By AtrreD Harker, M.A., F.G.S., 
Fellow of St. John’s College, Cambridge. 
jie the first paper of ‘this series® were described several dykes 
from the shores of the Menai Straits, belonging apparently to 
one system of intrusions, and some of them cutting Carboniferous 
strata. Their precise age, however, can be fixed only on the suppo- 
sition that they may fairly be correlated with certain post-Carboni- 
ferous but pre-Permian dykes in the Anglesey Coal-field. These 
latter rocks have a strong general resemblance to the Menai Straits 
dykes, and as they are by no means easily accessible, they will not 
be described in detail. Only one will be selected, as offering a 
1 L. Dollo, “ Huclastes,” ete. (loc. cit.). 
2 « On the Relations between Athece and Thecophora,” see L. Dollo, “ Chéloniens 
oligocénes,’’ etc., p. 83. 
3 A. Rutot, “Sur la position stratigraphique des restes de Mammiféres recueillis 
dans les couches de 1’Eocéne de Belgique,’ Bull. Acad. Roy. Belg. 1881, t. i. p. 22. 
4 L. Dollo, ‘‘ Chéloniens landéniens,”’ etc., p. 188. 
_° Grou. Mac. Dec, III. Vol. IV. p. 409, 1887. See also op. cit. p. 546. 
