102 ASTRODON.—TOMODON. 
The measurements of the longer specimen are as follows :— 
Inches. Lines. 
Extreme length . : : ' 5 : : : : : as 10 
Breadth of proximal end : 1 6 
Depth of proximal end at middle line . ; ; : . Zl vf 
Depth of proximal end to a level : : : : : 5 pe 
Breadth of distal end . 1 2 
Depth of distal end laterally 1 3 
ASTRODON. 
Astrodon Johnstoni. 
Astrodon, Jounston, American Journal Dental Science, 1859. 
Dr. Christopher Johnston has submitted to my inspection the greater part of a 
tooth, and a transverse section of another prepared by him for microscopic exami- 
nation, of an extinct Reptile, for which he has proposed the name of Astrodon. 
The specimens of teeth were obtained by Mr. Tyson from an iron ore bed, consi- 
dered as belonging to the Cretaceous epoch, near Bladensburg, Maryland. 
The tooth of Astrodon, of which four views are given in Figs. 20-23, Plate 
XIII, bears considerable resemblance in form to the teeth referred to the Hylco- 
saurus, an associate of the Jguanodon and Megalosaurus, in the Wealden formation 
of Europe. The specimen comprises nearly the length of the crown, and is about 
an inch and a half long. The shaft of the crown is straight, compressed cylindroid, 
in transverse section ovate, the outer side strongly convex, the inner side much less 
so. The summit of the crown is compressed conical, curved inward, convex exter- 
nally, depressed internally and sub-acute at the lateral borders, one of which is 
worn in the specimen so as to expose a narrow tract of dentine. 
The transverse section of the tooth beneath the microscope, as represented in 
Fig. 10, Plate XX, exhibits an interior disk of dentine, with a multitude of minute 
tubuli radiating from the narrow elliptical section of the pulp cavity, surrounded by 
a thick layer of enamel. 
TOMODON. 
Tomodon horrificus. 
Among some teeth of Sharks, from Mullica Hill, Gloucester County, New Jersey, 
in the collection of Dr. William B. Atkinson, I observed a tooth different from any 
I had previously seen, from the Green-sand formations. ‘The specimen represented 
in Figs. 7, 8, 9, Plate XX, Dr. Atkinson presented to the Academy of Natural 
Sciences. It appears to be the tooth of a gigantic carnivorous Reptile, a fitting 
contemporary of the Hadrosaurus. 
The base of the specimen is broken away, and exhibits the remainder of the 
pulp cavity, which is small and of the form of the exterior of the tooth. The apex 
also is somewhat injured, though I have been unable to determine how much of 
the bluntness of the specimen is due to accident. It has the appearance as if it 
