2l8 
F. Cavers. 
The curious genus Petalophyllnm (8, 48, 69) is closely allied to 
Fossonibronia, but in vegetative structure it strongly resembles 
Geothallns. The plant is fan-shaped, expanding from a narrow 
cylindrical basal portion. On either side of the stem there is a 
Fig. 40. Petalophyllnm ralfsii. Plant as seen from above. xS. 
Fig. 41. Petalophyllnm ralfsii. Transverse section through the middle of 
the leaf-bearing region of the plant. L., leaves; M., mycorhiza; Rh., 
rhizoids, X 20. 
horizontal wing bearing vertical laminae, which run forwards and 
outwards (Figs. 40, 41). The lamellae are one cell thick and are 
often arranged with great regularity in two series, one on cither 
