136 



LYCOPODIALES 



[CH. 



decorticated axes showing remains of Lepidodendroid leai- 

 cushions. The spirally disposed circular scars in the specimen 

 of Halonia {Lepidophloios scoticiis^) shown in fig. 160 constitute 

 the characteristic feature of the genus ; they may have the 

 form, as in fig. 160, A, of circular discs with a central umbilicus 

 marking the position of a vascular strand, or, as in the sand- 

 stone cast of Halonia tortuosa shown in fig. 161 ^ they may 



Fig. 161. Halonia tortuosa L. and H. From a specimen in Dr Kidston's Col- 

 lection, from the Lower Coal-measures of Ayrshire (No. 1561) ; | nat. size. 



appear as prominent tubercles. The latter example illustrates 

 the condition characteristic of partially decorticated stems. 



In 1883 Williamson^ described a specimen, now in the Leeds 

 Museum, which convinced him that Halonia is merely a special 

 form of Lepidodendron concerned with the production of fertile 

 shoots or strobili. FeistmanteH also recognised that Halonia 



1 Kidston (93) PL ii. fig. 6. 

 3 Williamson (83=) A. PI. 34. 



2 ibid. (02) PL Liii. fig. 2. 

 •• Feistmantel (75)A. p. 193, Pis. xxxiv. — xxxvii. 



