82 HISTORY OF BRITISH FERNS. 



the receptacle than a proper investing membrane. A similar 

 membrane has been observed in the species. The sori, 

 both in P. alpesti'e itself, and in the vsiviety fea:ile, are not 

 in all cases strictly punctiform, but occasionally, though 

 rarely, lateral but hardly elongated on the veins ; and this 

 is perhaps vihut induced Mr. Newman to propose the 

 genus Pseudathyrium. We, however, agree with those 

 who retain the plant in the Polypody family, and regard 

 flexile rather as a variety than as a species, though it is 

 certainly a remarkable one. This very interesting plant 

 was found in Glen Prosen, in 1852, by Mr. Backhouse 

 and Mr. Westcombe ; and the same botanists again found 

 it plentifully in the same district of the Clova Mountains, 

 in the summer of 1855. 



Genus 11. ALLOSORUS, or BOCK BRAKES. 



Of this family we have but one British species, the 

 Allosorus crispus. It is known from all its fellow-country 

 ferns by the coincidence of the following features. It bears 

 fronds of two kinds, one being leafy and barren, i. e. with- 

 out sori, the other contracted, and bearing sori ; and hence 



