PURBECK FORMATION. 35 



The dermal scutes agree in proportional size with the vertebra ; they are 

 subquadrate, smooth, and slightly concave on the inner surface ; they are 

 impressed with small, round pits on the outer surface ; of two scutes in apparently 

 natural juxtaposition, one slightly overlapped the other. 



The length of the dentary bone of Macellodon, above described, is 9 lines, or 

 17 millimetres ; the breadth of the neural arch across, and including the diapo- 

 physes, is 10 lines; the long diameter of a scute is 9 lines; its short diameter 

 6 lines. On the supposition, raised by the collocation in the same slab of these 

 remains, that they may have been parts of the same animal, we should recon- 

 struct, in idea, a Lacertian with a proportionally small and short -jawed head, and 

 with a skin defended by crocodilian scutes ; but I have seen similar scutes acci- 

 dentally associated, in another block of Purbeck clay, with mammalian jaws and 

 teeth, and they may have no closer relation to Macellodon. 



The remains of small, lizard-like reptiles, with teeth more or less fitted for 

 piercing, cutting, or crushing the chitinous coverings of Articulata, are such as 

 might be expected in the marly shell-beds of the Purbeck series, which have 

 afforded such abundant evidence of insect life;* and with them are associated 

 remains of small, insectivorous mammals. f The numerous remains of plants in 

 the same formation, some referable to Cycas, others to Zamia, illustrate also the 

 interdependency between the insect class and the vegetable kingdom. Amongst 

 the numerous and various Entomophaga organized to pursue and secure the 

 countless and diversified members of Insecta, in the air, in the waters, on the 

 earth, and beneath its surface, bats, lizards, shrews, and moles now carry on 

 simultaneously their petty warfare, and in warmer climates in the same localities. 

 In like manner, we now have evidence that lizards and mammals co-operated in 

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

 life during the deposition of the Lower Purbeck beds. 



Genus — EchinodonJ Ouen. 



EcHiNODON Becklesii, Owen. Tab. VIII, figs. 1—9. 



The specimens figured in the above-cited plate were discovered by S. H. 

 Beckles, Esq., F.R.S., in the thin, fresh-water stratum, containing shells^ and 



* See the paper by Mr. Westwood, in the ' Quarterly Journal of the Geological Society,' 1854, 

 p. 378. 



t See my paper on Spalacotherium, ib., p. 426. 



X 'F^xtvos, hedgehog, and ofous, tooth, " prickly tooth." 



§ Species of Valvata, Limneus, Cypris, and Physa, apparently Physa Bristovii. 



