648 NEW SPECIES OF MAMMALIA 



the Spalacotheriam. The average thickness of this stratum called No, 

 93, or the "dirt-bed," is about 5 inches.'^' It lies at the base of the 

 middle Purbeck, and consists of a soft marl, or calcareous mud, and con- 

 tains the remains of a few insects with freshwater shells of sfevei'al genera 

 (^Paludina, Planorbis, and Cyclas)^ and many reptiles. As the fruit of 

 his second day's excavations (Dec. 11th) Mr. Beckles sent me the lower 

 jaw of a mammal of a new genus, a discovery soon followed by others 

 in rapid succession, so that at the end of three weeks there were disin- 

 terred from an area not exceeding 40 feet in length by 10 feet in width, 

 the remains of five or six new species belonging to three or four distinct 

 genera, varying in size from that of a mole to that of a hedgehog, be- 

 sides the entire skeleton of a crocodile, the shell or carapace of a fresh- 

 water tortoise, and some smaller reptiles. AVhile these investigations 

 were in progress, Mr. W. R. Brodie of Swanage kindly forwarded to 

 me at my request the fossils which he had been accumulating during 

 two years (1855 and 1856) from the same thin bed in a contiguous area 

 no less limited in its dimensions. Besides reptilian remains, there were 

 among his acquisitions three lower jaws of three mammalian species, 

 and Dr. Falconer, who intei-preted for me the meaning of these and 

 other fossils, as they arrived from day to day, called my attention to one 

 slab in which was seen the upper portion of a skull, consisting of the 

 two parietal bones in a good state of preservation, with the sagittal 

 crest well marked, as also the connection with the frontals and the oc- 

 cipital crest. Although the lateral and basal portions of this cranium 

 are wanting, enough remains to show that it agrees with the ordinary 

 type of living warm-blooded quadrupeds, implying probably a higher 

 organization than that of such genera as the Stonesfield Phascolotherium 

 and Amphither'mm^ though affording no clear evidence whether the 

 creature was placental or marsupial. It is singular that this specimen 

 should have been the first example ever seen of a cranium, or indeed of 

 any part of the skeleton of a mammifer other than a lower maxillary 

 bone with teeth, from rocks more ancient than the tertiary. It supplied 

 therefore a more significant kind of evidence to the osteologist than had 

 previously been obtained of the exact correspondence in structure of 

 the mammalia of ft very remote period with the higher types of living 

 vertebrata. 



In the same slab with the cranium is one entire side of a lower jaw 

 of a quadruped, for which Professor Owen proposes the generic name 

 of Triconodon. It contains eight molars, a large and prominent canine, 

 and one broad and thick incisor. This creature must have been nearly 

 as large as the common hedgehog.f 



* This so-called "dirt-bed" is designated as No. 93 both in the Guide to the 

 Geology of the Isle of Purbeck, by the Rev. G. H. Austen (1852), and by the 

 Eev. 0. Fisher, in his paper on the Purbeck strata. Trans. Cainb. Phil. Soc, 

 vol. Ix. (1855). It has not the character of an ancient vegetable soil, as the 

 name would seem to imply. 



f The compressed crowns of the inferior molars in this Triconodon have each 



