Ch. XX.] FOSSILS OF THE MIDDLE PURBECK. 381 



series. It will be seen that Cyprh.fasciculata (fig. 371, b) has tuber- 

 cles at the end only of each valve, a character by which it can be 

 immediately recognized. In fact, these minute 

 crustaceans, almost as frequent in some cf the Fi s- 3T2 - 



shales as plates of mica in a micaceous sand- 

 stone, enable geologists at once to identify the 

 Middle Purbeek in places far from the Dorset- 

 shire cliffs, as, for example, in the Yale of 

 Wardour, in Wiltshire. Thick siliceous beds 



of chert occur in the Middle Purbeek filled _„ „ .. „ „ ■ 

 . . .. _ n . Physa JBrtstowt, E. Forbes. 



with mollusca and cyprides ot the genera Middle Purbeek. 



already enumerated, in a beautiful state of 



preservation, often converted into chalcedony. Among these Pro- 

 fessor Forbes met with gyrogonites (the spore-vessels of Charce), 

 plants never until 1851 discovered in rocks older than Eocene. 



Fossil Mammalia of the Middle Purbeek. — In the fourth edition of 

 this work (1852'), after alluding to the discovery of numerous insects 

 and air-breathing mollusca in the "Purbeek," I remarked that, 

 although no mammalia had then been found, " it was too soon to infer 

 their non-existence on mere negative evidence." Only two years 

 after this remark was in print, Mr. W. R. Brodie found in the Middle 

 Purbeek, about twenty feet below the " Cinder " above alluded to, in 

 Durdlestone Bay, portions of several small jaws with teeth, which 

 Professor Owen, after clearing away the matrix, recognized as belong- 

 ing* to a small mammifer of the insectivorous class. The teeth with 

 pointed cusps resemble in some degree those of the Cape Mole 

 [Chrysochlora aurea) ; but the number of the molar teeth (at least ten 

 in each ramus of the lower jaw) accords better with some of the ex 

 tinct mammalia of the Stonesfield Oolite (see below, p. 406). This 

 newly-found quadruped, therefore, seems to have been more closely 

 allied in its dentition to the Amphitherium (or Thylacotherium) than 

 to any existing insectivorous type. The angular process of the jaw, 

 as in Amphitherium, is not bent inwards, an osteological peculiarity 

 confined to the marsupial tribes, and Professor Owen therefore at first 

 referred the Spalacotherium to the placental or ordinary monodelphous 

 mammalia. 



Four years later (in 1856) the remains of twelve or more species 

 of warm-blooded quadrupeds were exhumed by Mr. S. H. Beckles, 

 F.R.S., from the same thin bed of marl near the base of the Middle 

 Purbeek. In this marly stratum many reptiles, several insects, and 

 some freshwater shells of the genera Palicdina, Planorbis, and Cyclas 

 were found. 



Mr. Beckles had determined thoroughly to explore the thin layer 

 of calcareous mud from which in the suburbs of Swanage the bones 

 of the Spalacotherium had already been obtained, and in three weeks 

 he brought to light from an area forty feet long and ten wide, and 

 from a layer the average thickness of which was only five inches, 



