432 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [June 7, 



the last five molars of this species have tricuspid crowns, with the an- 

 terior and posterior smaller cusps on a plane more internal than the 

 middle one, but the smaller cusps are given oflf nearer the summit of 

 the crown. These teeth also resemble the molars of the Spalacothere 

 in their small antero-posterior extent, but they are fewer in number 

 and are placed farther apart in the Cape Mole, which also is restricted 

 to the number of ten teeth in each ramus of the lower jaw, incisors 

 and canine inclusive. 



The Spalacothere has nearer affinities, as has been already inti- 

 mated, to the Thylacothere of the Stonesfield Oolite than to any 

 known existing species of Insectivore, and from the present evidence 

 I should place it in the same natural family of the Insectivorous order 

 of Mammalia. 



Touching the vdder question of the successive appearance of the 

 grades of animal life on this planet, the present acquisition from the 

 Purbecks in no way alFects the question as it was left by the long- 

 contested but finally settled evidence of mammalian life at the period 

 of the deposition of the oolitic slate at Stonesfield. 



Between that period and the oldest of the tertiary deposits, where 

 hitherto mammalian remains have next presented themselves in the 

 order of appearance, the interval is immense ; the lapse of time 

 having sufficed to allow of the deposition of the oolitic strata from 

 the Great Oolite upwards, of the "Wealden and Neocomian beds, and 

 of the formation, by more or less minute marine animals, of the major 

 part, if not the whole, of the carbonate of lime of which our Chalk 

 downs and cliffs consist. The chief interest in the discovery of the 

 Spalacotherium is derived from its demonstration of the existence of 

 Mammalia about midway between the older oolitic and the oldest 

 tertiary periods. 



Both the Oxford oolitic slate and the Purbeck marly shell-beds 

 give evidence of insect-life ; in the latter formation abimdantly, as 

 was shown in Mr. Westwood's paper read at a former meeting of 

 the Society*. The association of these delicate Invertebrates with 

 remains of plants allied to Zamia and Cycas is indicative of the same 

 close interdependency between the insect-class and the vegetable 

 kingdom, of which our power of surveying the phsenomena of life on 

 the present surface of the earth enables us to recognize so many 

 beautiful examples. Amongst the numerous enemies of the insect- 

 class ordained to maintain its due numerical relations, and organized 

 to pursue and secure its countless and diversified members in the air, 

 in the waters, on the earth and beneath its surface, bats, lizards, 

 shrews, and moles now carry on their petty warfare simultaneously, 

 and in warmer latitudes work together, or in the same locahties, in 

 their allotted task. • No surprise need therefore be felt at the disco- 

 very that mammals and lizards co-operated simultaneously and in the 

 same locality at the same task of restraining the undue increase of insect 

 life during the period of the deposition of the Lower Purbeck beds. 



The placental Insectivora are far from being the highest of the 

 Mammalian class, but at the same time they are not the lowest : if 

 * See above, p. 378. 



