104 Proceedings of the Royal Fhysical Society. 



also seen specimens from Bo'ness in Linlithgowshire (collec- 

 tion of Mr H. M. Cadell), Possil in Lanarkshire (collection of 

 Mr John Young), Cowdenbeath in Fife, and Maryhill near 

 Glasgow. 



These are large spines, some of which must have attained 

 a length of over 2 feet, had not their apices been worn off. 

 They always show some amount of lateral curvature ; but the 

 degree to which they are antero-posteriorly bent is very 

 variable; some are indeed in that direction nearly quite 

 straight. 



The first salient point which strikes the eye is the great 

 size of the inserted or non-sculptured portion, which is not 

 only broader and more expanded, but extends further beyond 

 the sculptured part proximally than in any other species. 

 The anterior middle line on which the gyrating ridges meet 

 does not cut equally the very acute angle formed proximally 

 by the sculptured part ; but in this case the larger division 

 is found on the subgibbous side, this being due to the 

 encroachment of the non-sculptured part on the gibbous 

 side. It is next to be noticed that the shaft of the spine 

 after the closure of the sulcus is more cylindrical than in 

 other species ; still the want of bilateral symmetry is very 

 obvious, and a gibbous and subgibbous side may be dis- 

 tinguished. The posterior groove is sometimes not apparent 

 for some distance after the closure of the sulcus, or, though 

 indicated, it may be filled with tubercles ; sooner or later it 

 becomes well marked, and the lip on the subgibbous side 

 becomes more prominent than the other, but does not form so 

 marked a feature in the configuration of the spine as the 

 corresponding posterior marginal keel in such species as G. 

 tuherculatus and nohilis ; it is in fact only towards the 

 extremity that the spine takes on a keeled appearance. A 

 well-marked row of recurved denticles occurs along the 

 aforesaid lip or ridge of the posterior groove on the subgibbous 

 side, and on that of the opposite side denticles are also seen 

 in some examples. The last remarkable feature in this 

 species is the slight obliquity of the gyrating ridges, which 

 meet each other on the front of the spine at angles greater 

 than right angles almost as far as the very apex. These 



