154 MR ROBERT KIDSTON ON THE FRUCTIFICATION OF 



On the other hand, when more perfect specimens are secured, the differences 

 between the fruiting portions of A. convoluta and C. Acadica and T. Collombi 

 are very well marked, and in the barren condition, the British species has no 

 similarity with either Schimper's or Dawson's plants. 



It may be questioned if this new plant should not be included in Rhacophyl- 

 lum, with which its barren pinnae have so great a resemblance, but against 

 adopting this course is the fact that Rhacophyllum is essentially a Coal Measure 

 genus, whereas A. convoluta has hitherto only been found in the Calciferous 

 Sandstones, and then usually in the basement beds. Whatever view may be 

 taken of the genus Rhacophyllum, whether as forming an individual genus or as 

 a provisional one, only containing the accessory pinnules of other ferns, I am 

 not in a position to decide ; but in regard to A. convoluta there can remain no 

 doubt as to its being an autonomous fern, and not a portion of another species. 



In Triphyllopteris Collombi the fruit is borne at the extremity of the 

 circinately bent segments, and it probably occupied a similar position on 

 A. convoluta, but none of the specimens that have come under my notice have 

 shown any traces of sporangia. 



Description of Specimens. — Specimen from Horncliffe Dean, near the Mill, 

 Eiver Tweed, South of Horncliffe Village, Northumberland, collected by Mr 

 J. Ehodes (Plate VIII. fig. 11), in the Collection of the Geological Survey of 

 England. This specimen shows a small portion of a barren frond. The rachis 

 is very stout, and gives off apparently alternate pinnse, possessing a midrib with 

 a sharp angular ridge. This example is not well preserved, and does not show 

 any perfect pinn?e or pinnules, but these were apparently cut into lobes, having 

 curious spirally twisted segments, which at their point of separation formed an 

 almost circular sinus giving the frond a curled appearance. 



Specimen from Eiver Tweed, 100 yards below Norham Castle, Northumber- 

 land, collected by Mr J. Ehodes (Plate VIII. fig. 12), in the Collection of the 

 Geological Survey of England. This specimen, though also fragmentary, is a 

 very good example of the mode of ramification of Alcicornopteris convoluta. It 

 exhibits a portion of a rachis 4 cm. long, and 5 mm. broad at the lower broken- 

 over extremity, and 1 cm. wide immediately below the point where it bifurcates. 

 The two arms of the first bifurcation go off from the parent rachis at almost 

 right angles, and then again bifurcate. Both the upper forks of this second 

 dichotomy arc broken over, but the lower arm on the left forms a third series 

 of dichotomies. On this is borne the barren pinnules. A portion of one of 

 the corresponding forks of the right hand dichotomy of the third series is also 

 present. Here again the pinnules are badly preserved, but show the same 

 characteristics as fig. 11. The rachis appears to have been flat, and traversed 

 by a prominent vascular system which appears as a triangular ridge. The 

 hclicoid nature of the frond is well shown on the frondose portion of this 

 specimen. An imperfect fragment of a pinnule lies between the primary forks 



