362 DK F. A. BATHER. 



Lower Mudstones : pale blue or greyish -green, often sandy, shales and flagstones : 



Dicellograptus anceps, Bellerophon bilohatus, B. trilohatus, B. perturhatus, 



Plectamhonites sericea, Trinucleus Bucklandi and other trilobites (see Reed). 



Basal Sandstones : flagstones with quartz pebbles, seams of grey and green 



shales : Fossils abundant, Plectamhonites sericea, " Strophomena." 



§ 7. It is clear from the fossils quoted that the Drummuck Group falls within that 



upper part of the Caradocian which Dr J. E. Marr (1905, p. Ixxxiv.) has proposed to 



distinguish as the Ashgillian Series. The Starfish Bed itself lies in or above the zone 



of Dicellograptus anceps, which is the highest zone in the Hartfell Shales of S. Scotland. 



It contains several species also found in the Keisley and Kildare Limestones, and 



appears to be the partial equivalent of the Killey Bridge beds in Tyrone (see 



Fearnsides, Elles, & Smith, 1907), the Rhiwlas Limestone of N. Wales, and of the 



top of the Sholeshook Limestone in S. Wales. The Keisley Limestone is now believed 



to correspond to the Leptaena Kalk of Dalecarlia, which Swedish geologists correlate 



with the Brachiopod Shales of Vestrogothia, and approximately with the upper part of 



the Upper Lyckholm (F 1 ) in Baltic Russia and the Coral Limestone of Ringerike in 



Etage 5 of the Christiania district (see Warburg, 1910, p. 435). The corresponding 



horizon in Bohemia falls within D5 of Barrande = 2d of Katzer (1889, 1902). 



§ 8, The Starfish Bed, as its name implies, is prolific in Echinoderms. In addition 

 to Tetraster Wyville-Thomsoni, there are many Asteroidea, now being studied by 

 Mr W. K. Spencer. Hitherto, however, the only published references to Cystidea have 

 been the record of Pleurocystis* sp. by Mrs Gray (1899, p. 687), and by Peach, 

 HoRNE, & Macconochie (1901, p. 431). Perfect specimens, it is true, are rare; but 

 fragments are exceedingly numerous, and Mrs Gray fortunately appears to have 

 collected all that she could lay her hands on. Thus one is enabled little by little to 

 piece together the complete structure of various species. And it should be mentioned 

 as worthy of high commendation that Mrs Gray has always done her best to obtain 

 both counterparts of each specimen. This is by no means always possible ; but when 

 specimens are preserved, as they are here, entirely in the form of their imprint or 

 mould, then the possession of both sides of the mould is of the highest value to the 

 palaeontologist. In this respect Mrs Gray's collection compares most favourably with 

 the material from Bohemia, with which I have so frequently had to compare it. I 

 emphasise this point because in past ages people seem to have thought nothing of 

 keeping a counterpart in one country and sending its fellow to a distant country (see 

 § 468). We are fortunate indeed if in such a case two diff'erent species are not founded 

 upon the parts of a single individual. 



§ 9. But, though the Cystidea of the Starfish Bed are numerous in individuals, the 

 number of species is small. I describe only nine, of which eight are new, and it is 

 quite possible that some future palaeontologist will say these are twice as many as they 

 ought to be. 



*• Miaprinted " Protocystites" on p. 526 of the Geol. Surv. Memoir on the Silurian Rocks of Scotland, 1899. 



