2 BRITISH PALEOZOIC ASTEROZOA. 



respect to fossil plants applies with equal force to fossil Asterozoa. " What 

 the record really shows is a succession of dominant groups, each of Avhich reached 

 a very high development in its time, and then, as the conditions changed, fell into 

 the background, some new family springing ujd to take its place," 



MATERIAL AND METHOD. 



I have Ijeen A'ery fortunate in having excellent new material placed at my 

 disposal. 



The material preserved in London Museums is scanty and often indifferently 

 preserved, and previous observers have had to rely mainly upon these specimens 

 for their descriptions. Mrs. Gray, of Edinburgh, has for many years made 

 an extensive collection from the Ordovician of Girvan. There is also a large 

 collection from the Silurian of Ayrshire in the Scottish National Museum of 

 Edinburgh. Both these collections were kindly lent to me, and together they 

 contain upwards of five hundred specimens — a great number considering the age of 

 the rocks. 



The collection of Mrs. Gray is especially valuable, great care having been taken 

 to obtain both counterparts of each fossil. The specimens are preserved as 

 moulds in a fine sandstone, and very clearly cut casts can be obtained which may 

 show even the fine ornament of the original ossicles. The casts are usually much 

 easier to interpret than are specimens preserved in the original calcite. They 

 have been studied by means of a binocular stereoscopic microscope. The ossicles 

 of the original fossil are often fused by solution and re-dejjosition of the calcite, 

 and the boundary line between component plates cannot then be distinguished. 



New material has also been investigated from the well-knowm Leintwardine 

 (Lower Ludlow^) mudstones, preserved in the Ludlow Museum, the Scottish 

 National Museum, the collection of the Rev. W. D. La Touche, of Winstanton 

 Rectory, and the collection of Mr. Beale, of Leintwardine, Apparently casts had 

 not previously been made from this material, and in consequence it has been 

 possible to identify some delicate structures which had been destroyed on the 

 specimens preserved in the London Museums. It will be remembered that one pit 

 at Leintwardine has yielded by far the greater number of Asterozoa which have 

 been obtained from English Silurian rocks, and it has been of great advantage to 

 obtain these fresh supj)lies. 



I have also re-investigated the collections in the British Museum (Nat. Hist.), 

 London, the Museum of Practical Geology, Jermyn Street, London, and the 

 Sedgwick Museum, Cambridge. The British Museum (Nat. Hist.) not only 

 contains specimens from British rocks, but also the valuable type-specimens 

 from the Lower Devonian of Bundenbach, Germany, collected and described 



