Freshwater Limestone in Forfarshire, S^c. 93 



The short bristly prickles which distinguish the stems of C. hispida are so 

 easily detached, that they can scarcely be preserved even in dried specimens, 

 and are always wanting- in the fossil. 



C. vulgaris. — This plant inhabits the Bakie and other lakes in Forfarshire, 

 Although I have not yet met with its seed-vessel fossilized in the rock-marl^ 

 yet I cannot doubt that it exists there : for in that rock a large quantity of 

 fossil stems are found, agreeing exactly in size and appearance with those of 

 C vulgaris, which are not above half the diameter of those of C. hispida. 

 They are scarcely otherwise distinguishable, except that the striae are less 

 deeply indented. 



The seed-vessel is smaller and more obtuse than that of C. hispida (see 

 PI. XII. fig. 3. a, b.) ; but the spiral valves form the same number of rings. 

 Dr. Brewster states that carbonate of lime occurs crystallized according to a 

 regular arrangement beneath the cuticle of the stem of this species. [Edin. 

 Phil. Journ. Jan. 1823. No. 17. p. 194.] 



C.Jlexilis*} — A figure of this species is added, as it inhabits most of the marl 

 lakes in Forfarshire, though not found in the Bakie. The spiral valves of the 

 seed-vessel turn each about 2j; times round the circumference, the whole 

 together forming about 13 rings, which exceed the number in C. hispida and 

 vulgaris. (See PI. XII. fig. 4. a, b.) 



CMedicaginula (fossil). — The external integument of this species is figured 

 by M. Brongniart. [Oss. Foss. 2d edit. vol. ii. PI. XI. fig. 7,] The present 

 section is taken from one occurring in the lower freshwater formation at Gur- 

 net Bay in the Isle of Wight. It exhibits the fossilized nut as inclosed in the 

 integument, more distinctly than in any specimens which I have seen from the 

 Paris Basin. (See PI. XIII. fig. 2. b.) The integument frequently adheres 

 to the stone, while the nut is easily detached. (See PI. XIII. fig. 3, 4, 5.) 



It will be remarked that in these three specimens the number of the ribs or 

 striae on the nut varies from 5 to 7 ; yet it is possible that they are referrible 

 to the same species ; a point which cannot be decided until more botanical 

 knowledge has been acquired on the fructification of this tribe of plants. Fig. 5. 

 PI. XIII. represents one from the same group which is more elongated, but 

 of which the shape has perhaps been distorted. As the number of ribs are 

 nine, and the intermediate striae are wanting, it may belong to a distinct spe- 

 cies. 



A drawing of a fossil stem accompanying the above-mentioned gyrogonites 



* Charajlexilis, here alluded to, has been recognised by Dr. Hooker as the C.Jlexilis of his 

 Flora Scotica; but he has observed in that work, that botanists have experienced considerable dif. 

 ficulty in distinguishing the Charae. 



