72 On the chief Oeneric Tyi?es of Palaeozoic Corals. 



The genus Rhodophyllum, so far as our present knowledge 

 goes, is exclusively confined to the Carboniferous period, and 

 it has not hitherto been recognized out of Scotland. Though 

 very readily recognized in typical examples, it is, as before 

 said, united with its immediate allies by transitional forms. 

 The best-marked of these intermediate groups is to be found 

 between typical examples of Rhodophyllum on the one hand, 

 and Aspidophyllum on the other hand. The figures in 

 Plate III. represent longitudinal and transverse sections of 

 this intermediate and transitional type. In this group the 

 vertical lamellse of the central area do not exhibit that con- 

 tortive arrangement which is so characteristic of Uhodophyllum^ 

 but they are generally seen in transverse sections (diagr. D) as 

 irregular, more or less wavy lines, often uniting with one 

 another in a series of undulating curves, the convexities of 

 which are directed centrally. There is no single predominant 

 vertical lamella, such as exists in Aspidophyllum \ but the 

 cut edges of the tabulse are seen in transverse sections to have 

 much the same arrangement as in the latter genus, being 

 strongly curved, and having their convexities directed inwards. 

 In longitudinal sections (PL III. figs. 1 & 5 a), the central area 

 is seen to be occupied with anastomosing and closely vesicular 

 tabulge, intersected by several irregular and discontinuous 

 vertical lines, representing the cut edges of the vertical 

 lam elite. 



EXPLANATION OF THE PLATES. 



[Unless otherwise stated, all the figures are of the natural size. 

 In these three plates we have tried the experiment of printing the figures 

 in white upon a black ground. It may he questioned, however, if the 

 results are quite so satisfactory' as in the ordinary method of printing in 

 black on a white ground.] 



Plate I. 



Fig. 1. RhodophyHum Slimonianum, Thomson, transverse section. Lower 

 Carboniferous, Brockley, near Lesmahagow. 



Fig. 2. Ehodophylhm Phillipsianmn, Thomson, transverse section. Lower 

 Carboniferous, Trearae, near Beith, Ayrshire. 



Fig. 3. Rhodophyllum Craigianum, Thomson, transverse section ; 3 a, lon- 

 gitudinal section of the same. Lower Carboniferous, Trearne, 

 near Beith, Ayrshire. 



Fig. 4. RhodophyUinn simplex, Thomson, interior of an imperfect calice, 

 showing the form of the central boss; 4 A, transverse section of 

 the same. Lower Carboniferous, Brockley, near Lesmahagow, 



Plate II. 



Fig. 1. Rhodophyllum Phillipsianum, Thomson, transverse section ; 1 a, 

 longitudinal section of the same. Lower Carboniferous, Lang- 

 side, near Beith, Ayrshire. 



