BKITISH FOSSILS. 



The llth segment, tigs. 3, 4, suddenly changes shape, it is half 

 oval, with both ends truncate, and its length is rather more than 

 three-fourths of the width. The base is contracted, the sides curve 

 boldly outwards, and again contract at the produced and hooked 

 posterior angles. The segment is thus much broadest behind. We 

 have both upper and under surfaces, the former is carinated all the 

 way down by a strong median ridge, wider and less prominent at 

 first, then sharply elevated and covered with coarse squamse. The 

 under side, fig. 3 6, has no median ridge except for its middle 

 third, and this, which begins by a gentle elevation, ends abruptly 

 rather more than two-thirds down. It is closely covered with large 

 squamae, and probably indicates the place of the anal opening. The 

 lateral and posterior margins are also bordered with tubercular 

 squamse, largest and most conspicuous on the sides. Our finest 

 specimen is three inches and three-quarters long, and four inches 

 and a quarter wide behind the middle, where the width is greatest ; 

 at its upper end it is only two inches and a quarter broad. 



In the same beds, near Forfar, penultimate joints occur, which 

 are probably of the same species, but show a marked difference 

 from those in the plate. An upper and under side is here figured. 



A the upper side, 

 and B the un- 

 der, showing 

 the anal ridge 

 a. Base of 

 Old Red Sand- 

 stone, Leys- 

 mill, Forfar- 



