358 T'ransactions.— Geology. 
of the section are wanting, and the upper, or chalk, group is found to rest 
against the older sandstone rocks of the district. In the estimated thickness 
of 2,500 feet of strata exposed at the Amuri Bluff, it is evident, from the 
fossils, that the sub-divisions as above may be, at least provisionally, adopted 
with advantage. The only fossil that appears to be common to the second 
and third groups is Trigonia sulcata,* and unless No. III. is the equivalent 
of the Belemnite beds at Waikato Heads and Kawhia, it has not yet been 
found at any other part of the colony than the Amuri Bluff. If it is the same 
formation the evidence obtained from the above section would seem to require 
the sub-division of the Putataka beds into two distinct formations. 
Акт. LHI.—0On the Teeth of the Leiodon. Ву Cuartes Кмівнт, F.R.C.S., 
President of the Wellington Philosophical Society. 
Plates XXIV.—XXVI. 
[Read before the Wellington Philosophical Society, 16th January, 1874.] 
AT the suggestion of our late President, Dr. Hector, I have examined 
microscopically the fossil teeth of the remains of the Leiodon in the Museum. 
The aquatic Saurians are arranged under Sauropterygia and Pythono- 
morpha. The former had two pairs of limbs, the latter an anterior pair 
only. The Leiodon belongs to the Pythonomorpha, with snake-like bodies 
of immense length. The Z. dyspelor, discovered in New Mexico, is estimated 
at not less than 100 feet in length, and would be, says Professor Cope, the 
longest reptile known, and may well excite our astonishment. 
The Leiodon is closely allied to the celebrated gigantic Mosasawrus hoff manni, 
or what was at first called the crocodile of Maestricht. Neither Mantell nor 
Owen were able to say, from the few and scattered remains to which they had 
access, whether the Leiodon is a species of Mosasaur or a distinct genus. The 
chief distinction is in the teeth, which, in the Mosasaur, have the outer side 
flat with two sharp edges, while the inner side is round. Where the teeth 
are absent the unsettled distinction between the Mosasawr and the Leiodon 
renders it probable that some of the former species may really be Leiodon, as 
suspected by Professor Cope in his paper on the fossil reptiles of the cretaceous 
* Trigonia sulcata, n. sp. General form like 7. gibbosa, but sculpturing different. 
Traversed radially by a wide groove; ; posterior area with radial striæ ; anterior with 
divaricate rens cut into tubercles by concentric striæ, that are continued over the 
whole surface. Valve rather flat ; wing ri dod rounded and overhanging ; hinge- 
plates strong. Length, 35 inches ; width, 3 
