450 5 
Teeth from the same formation at Maidstone, referable to the genus 
Polyptychodon,” by Richard Owen, Esq., F.G.S. 
The fossil saurian remains from the lower greensand discovered 
by Mr. H. B. Mackeson include portions of ‘the iliac, ischial and 
pubic bones, a large proportion of the shaft of a femur, parts of a 
tibia and fibula, and several metatarsal bones. In consequence of 
the absence of vertebra and teeth, the determination of the specific 
characters of this Saurian is, the author states, a subject of great 
difficulty, and he therefore confines his remarks, in the present paper, 
to indications of the. characters by which it differs from previously 
known extinct genera of Saurians.. In the first place, Mr. Owen 
shows, from the femur and other long bones having no medullary 
cavities, but a central structure composed of coarse cancelli, that 
the animal of which they formed’ part was of marine habits; he, 
however, adds, that the principal bone beimg a femur, independently 
of the size and shape of the metatarsals, at once| negatives the idea 
that these remains belonged to the cetacean order; and that the 
form and proportions of the metatarsals equally forbid their reference 
to any other mammalian genus. : 
Jremur.—The portions of this bone secured by Mr. Mackeson in- 
clude about the two distal thirds, excepting the articular extremity. 
Its length is two feet four inches, its circumference in the middle or 
smallest part of the shaft is fifteen inches six lines, and at the broken 
distal end, two feet five inches. ‘These dimensions prove that the 
animal was equal to the most gigantic described Iguanodon*. If 
the supposition of the proportion of the femur which has been pre- 
served be right, this bone, Mr. Owen says, differs from that of the 
Iguanodon, not only in the want of a medullary cavity, but also in 
the absence of the compressed second trochanterian process which 
projects from the outer side of the middle.of the shaft, and which 
forms one of the several curious analogical relations between the 
Iguanoden and Rhinoceros. The bone also expands more gradually 
than in the femur of the Iguanodon, and the posterior part of the 
condyles must have been wider apart in consequence of the posterior 
inter-condyloid longitudinal excavation being longer and wider. Va- 
rious other minor points of difference are noticed by the author. 
Tibia and Iibula.—The portion of a tibia which has been preserved 
is compressed near its head, and the side next to the fibula is slightly 
concave. The longest transverse diameter is eight inches nine lines, 
and the two other trausverse diameters at right angles to the pre- 
ceding give respectively three inches three lines and two inches six 
lines. The bone soon assumes a thicker form, its circumference at 
about one-third from its proximal end being sixteen inches six lines. 
The cancelli occupying the central portion of the bone are arranged 
in a succession of layers around a point nearest the narrower end 
of the transverse section. Lower down the tibia again becomes 
compressed, and towards the distal end the transverse section exhi- 
* Femur of the [guanodon,—length, 4 feet 6 inches ; smallest circum- 
ference, 1 foot 10 inches, ; 
