PURBECK BEDS. 345 



tree-Stumps are still erect, with their roots in the soil, but they 

 are broken off a short distance from the ground. He observes that 

 a submergence, or change of level, converting the lands on 

 which the trees grew into a morass, would inevitably cause the 

 destruction of the forest, and occasion a rapid decay, especially at 

 the bases of the trees, and, thus weakened, they would yield to the 

 force of wind or flood, and break off" a few inches from the root.^ 



The Cycads include Yatesia gracilis, Bcnnettites Portlafidicus, 

 Mantellia nidiformis, M. intermedia, M. microphylla, and M. pygmaa} 

 The plants include also the Conifer, Dammarites Fittoni, and seed- 

 vessels of Chara. 



In 1854 Messrs. Wilcox and W. R. Brodie of Swanage discovered 

 the Mammal Spalacotherium tricuspidens, in a thin carbonaceous bed 

 at the base of the Middle Purbeck beds at Durlston Bay. Later 

 on, in 1856, chiefly owing to the labours of Mr. S. H. Beccles, who 

 opened a quarry in the cliff's, many remains of marsupial Mammalia 

 (insectivorous, predaceous, and herbivorous) were found. These 

 include Ainphitheriiun, Plagiaulax, Stylodon, etc. Altogether 

 thirteen genera and twenty-four species of Mammals have been 

 identified by Sir Richard Owen and Dr. Falconer.^ More recently 

 (1880), from the same pit, known as 'Beccles' Quarry,' Mr. E. W. 

 Willett obtained a specimen of Triconodon ?7iordax} The Reptiles 

 obtained from the Purbeck Beds include the Swanage Crocodile, 

 Goniopholis crassidens, also Macrorhynchus, the Lacertilian Nuthetes 

 destructor, and Pterodactylus ; as well as the Turtles Pleurosternon 

 concinnum, Chelone obovata, etc. These occur in the Upper and 

 Middle divisions of the Purbeck Beds. Fish-remains are not 

 uncommon in the same divisions ; they include Lepidotus minor, 

 Microdon radiatus, Hybodus strictus, Asteracanthus, PholidopJiorus 

 granulatus, etc. Batrachian remains have also been recorded. 



The principal Mollusca have been previously noted, as well as 

 the Hemicidaris discovered by Prof. E. Forbes. Among other 

 fossils the Isopod Archcwiiiscus is abundant in some localities ; and 

 Ostracoda are also of frequent occurrence. Cypridea pimciata 

 characterizes the Upper Purbeck Beds ; C . granulosa, vox.fasciculata, 

 the Middle Beds ; and Cypris Purbeckensis the Lower Beds.^ A 

 fresh-water sponge (Spongilla), from the Purbeck Beds at Lulworth, 

 has been described by Mr. J. T. Young.^ 



Insect-remains are plentiful in the Middle and Lower Purbeck 

 strata ; they include chrysalides of Lepidoptera, Wings of Libellula, 

 and of Dipterous and Hemipterous insects, and elytra of beetles. 



1 Proc. Dorset Nat. Hist. Club, ii. i ; see also G. Mag. 1873, p. 410. 



^ Carruthers, T. Linn. Soc. xxvi. 675. The old genera identified as Zamites 

 and Cycadites are now regarded as Jllantellia. 



2 See Owen, Fossil Mammals (Palreontograph. Soc.) ; Falconer, Q. J. xiii. 261. 

 An animal allied to Plagiaulax has been found in the Jurassic rocks of Wyoming, 

 and in the Lower Eocene of Rheims. 



* Q. J. xxxvii. 377. 



5 T. R.Jones, Q. J. xli. 311. 



^ G. Mag. 1878, p. 220. 



