234 HISTORY OF BRITISH TERNS. 



greyish ring, variable in position, being sometimes central, 

 arid at other times near the base or near the margin ; it 

 is, however, we believe always, much less decided and 

 clearly defined than the pale-coloured band on the sheaths 

 of E. hyemale. 



The section of the stem differs from that of E. hyemale, 

 to which it presents a general resemblance, in being smaller, 

 showing fewer ridges, and having the cavities placed rather 

 nearer the inner margin ; the central cavity is also propor- 

 tionally smaller. It has, consequently, on the exterior, a 

 series of ridges formed of twin projections representing the 

 double row of siliceous particles which extends along each 

 ridge ; and a series of cavities rather nearer the inner than 

 the exterior surface of the ring. 



The fructification consists of small black cone-like heads, 

 of an oblong form, terminating in an apiculus. In our 

 specimens they appear sessile in the upper sheath, but they 

 are said to become elevated on a short pedicel. The scales, 

 in one of these cones, number about thirty. 



Equisetum Mackayi is found on the moist banks of the 

 mountain glens of Scotland and the north of Ireland. It 

 was first found in Ireland, and apparently by two botanists 

 in company, Mr. (now Dr.) Mackay, and Mr. Whitla ; this 



