FROM THE ZONE OF AMMONITES ANGULATUS. 



41 



VI. Description of the Species from Lussay in the Isle of Skye. 



Dr. T. Wright has described the Coral-bed of the Lower Lias of Skye, and the species 

 of Isastraa which, grouped in masses, appears to be the only Coral found there. It is 

 most probable, from the position of this coral-bed,^ and the association of Osfrea arietis 

 and Cardinia concinna with it (in the bed beneath), that Isastraa Murchisoni belongs to 

 the same geological horizon as the Liassic deposit at Brocastle and the Sutton Stone. 



IsASTRiEA Murchisoni, Wright. PI. XI, figs. 1 — 4. 



Dr. Wright's description of this species gives the following characters : 

 Corallum large, massive, convex. Calices unequal, deep, polygonal ; sides unequal. 

 Margin thin. Septa, 30 to 36, and even 40 or more in the large calices ; unequal in 

 length, thin, waved, granulated superiorly. Columella absent ; point of convergence 

 of septa excentral. Diameter of calices, /gths to/oths inch. Depth of fossa, ^ths inch. 

 Locality/. Lussay, Skye. 



The surface of the type specimen is very uneven ; the calices are very irregular in 

 size, shape, and depth, and the margins are not even. Thus one calice may be on a higher 

 level than those to which it is attached, and often so much so that there is a faint trace 

 of a subsequent growth of wall. The septa are very irregular in their number, and the 

 longest have one or more teeth at their inner end. There is often a ridge between the 

 margin of the calice and the centre, indicating calicinal gemmation, but the gemmation 

 of the corallum usually takes place at the margin, and there is no fissiparity. No cyclical 

 arrangement of the septa can be distinguished. 



The large and shallow calices, thin septa, the peculiar relation of contiguous calices, 

 and the sharp elevated margins, distinguish this species, which is allied rather to a 

 new genus from the Middle Lias of Pabba, Lepidophyllia (Duncan), than to any of the 

 Liassic Isastrsese. 



' See Mr. Geikie's memoir "On the Geology of Strath, Skye;" with "Descriptions of Fossils," by 

 Dr. T. Wright, 1857, 'Quart. Journ. Geol. Soc.,' vol. xiv, pp. 1 et seq^. There is a most interesting 

 description of the Coral-bed in the Isle of Skye by Hugh Miller, in his " Essay on the Corals of the 

 Oolitic System of Scotland," read before the Royal Physical Society of Edinburgh, and published in 

 ' The Old Red Sandstone,' 7th edition, 1859. 



2 ' Quart. Journ. Geol. Soc.,' vol. xiv, p. 34. 



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