204 



Purbeck Beds. 



beck Limestone. It is chiefly formed of remains of the 

 delicate fresh-water univalve, Paludina fluviorum. 

 Many fish have been found in the Purbeck strata ; 

 among these, Lepidotus minor, Pholidophorus ornatus, 

 Microdon radiatus, Ophiopsis breviceps, Hybodus, 

 and Aster acanthus, are the most characteristic. 



Numerous wings, elytra, and other fragments of 

 insects (Coleoptera, Orthoptera, Hemiptera, Neuro- 

 ptera, and Diptera), occur in thin bands in the Pur- 

 beck Limestones. Some of these (dragon-flies, &c.) are 



FIG. 41. 



Physa Bristovi. 



Unio compressus. 



Ostrea distorta. 



Cyrena media. Cypris Valdensis. Paludina fluviorum. 



Group of Fossils from the Purbeck and Wealden beds. 



such as would live on the marshy banks of rivers. 

 Among the reptiles are Crocodilia viz., Goniopholis 

 crassidens, and Macrorhynchus ; Lacertilia; fresh- 

 water Tortoises, and Turtles viz, Pleurosternon con- 

 cinnum, P. emarginatum, P. ovatum, &c. 



In 1854, portions of the jawbone of a small mar- 

 supial insectivorous mammal, Spalacotherium tri- 

 cuspidens, were found by Mr. Brodie at the base of 

 the middle Purbeck beds. At the close of 1856, Mr. 

 Beckles commenced a further search in the same bed, 



