part 3] CHAROPHTTA or THE LOWEE HEADOjS^ BEDS. 181 



Chara Wriglifii, O. helicferes, and C. vasiformis being seen. 

 Other fossils, except Paludina and Unio, are not common. 



A conspicuous but thin sandy band crowded with seeds of 

 Liinnocarpus and Stratiofes is very noticeable east of Paddj^'s 

 Gap. It has jdelded also a few fruits of Chara, but they are not 

 very well preserved. 



Then follow thin bands of clay and sand, with Faludina, 

 Melaiiia furritisshna, and Unio; in these we have not observ^ed 

 any Cliarophyta. 



Bed 31 is the sand which now rises nearly to the top of the cliff 

 under the gravel. It was formerly followed by a band of cla}", and 

 this by a thin limestone (32) — the How Ledge Limestone ; but 

 these two beds, too-ethei* about 5 feet thick, have now entirely 

 disappeared, as has the marine Middle Headon last seen about the 

 year 1850. 



Paet II. 



Tlie remains of Charophyta, which afford the material for this 

 paper, consist of numerous detached fruits, some fragments of 

 stems and branchlets, and a few stem-nodes with portions of the 

 internodes of stems and the bases of the branchlets attached. There 

 are also a few bodies which are apjoarently the actual stem-nodes. 

 In no instance has a fruit been found attached to a branchlet, and, 

 owing to the fact that in each deposit more than one type of fruit 

 is present, it is not possible to identif}' any of the fruits with the 

 vegetative j^arts to which they belong. 



Fruits. 



The fruits, the remains of which are here preserved as fossils, 

 would appear to consist onl}^ of those which have developed a 

 * lime-shell," similar to that with which we are familiar in many 

 existing species of Chara and in a few of the Tolypellce. This 

 lime-shell is formed by the secretion of carbonate of lime of 

 extremely fine grain, in the interior of the five spiral cells which 

 constitute the wall of the oogonium. As the fruit matures the 

 lateral walls of the spiral cells, where they are in contact one with 

 the other, break down, and the calcareous contents of the five cells 

 combine to form one shell which surrounds the oospore. The 

 calcareous deposit goes on increasing, until it has almost entirely 

 replaced the original protoplasmic contents of the cells. That the 

 preservation of these fossil fruits is due to the presence of the lime- 

 shell may, we think, be fairly adduced from the following con- 

 siderations : — 



(1) The practical impossibility of large thin- walled cells being preserved 



in siich a formation if merely filled with protoplasm. 



(2) The fact that no evidently young fruits are found as fossils, and that 



in existing species the lime-shell only occurs in mature fruits. 



(3) The invariable absence in the fossils of the coronula and stalk-cell, 



which organs, in existing species, do not secrete calcium carbonate. 



(4) The great diversity in the thickness of the shell in the fossils, the 



