280 prof. w. j. sollas on ichnium [May 1900, 



.case ; the beaded appearance is most obviously displayed by those 

 specimens which exhibit no effects of pressure. 



The grooves of 0. radiata sink below the smooth even surface 

 of the phyllite, without any corresponding ridges to bound them at 

 the sides ; only in the case of one or two isolated linear grooves have 

 I seen a faint mound running parallel along each side (PL XIX, 



fig. 12). 



Of the two species of Oldhamia, 0. radiata most closely resembles 

 Ichnium Wattsii, but even this is distinguished by a multitude of 

 important details, its grooves are far more sharply defined, branched 

 incomparably more frequently, and they terminate in club-shaped 

 processes, which find no parallel in Ichnium. 



Oldhamia antiqua. (Pis. XYII-XIX.) 



It has been shown by Prof. Joly that while 0. radiata consists 

 •of a system of grooves, 0. antiqua, on the other hand, occurs as a 

 system of ridges. The assertion has been doubted, but there can be 

 no question as to its general truth ; Prof. Joly's specimens, which he 

 has kindly lent me for examination, fully bear out his statements. 

 The rule, however, is not, I think, absolute, for in one example of 

 0. antiqua, displaying most of the structure in relief, four of the 

 radiate processes are in depression. I owe to the kindness of 

 Prof. Joly the loan of the beautiful example of 0. antiqua, which 

 is represented by the accompanying photograph (PI. XVII, fig. 3). 

 A long broad ridge or stem, 12 mm. in length by 1 mm. in 

 breadth, resembling the trail of a worm, though in relief, expands as 

 it gives origin to the well-known fan- shaped system of appendages 

 of this species. The appendages do not arise immediately from the 

 swollen extremity of the stem, but from an ill-defined oval area, 

 which is far better marked in many specimens (PI. XIX, fig. 11) 

 than in this ; its surface is, as a rule, remarkably smooth and even ; 

 the appendages arise singly and abruptly just within its outer 

 margin. 



The appendages may be simple- or branch once or twice ; the 

 simple or final branches are more or less club-shaped and beaded, 

 after the same fashion as the grooves of 0. radiata, except that in 

 this case the beading is sometimes biserial. They are straight 

 or curved, rarely undulating, and have a suggestive appearance 

 of rigidity, such as may also be remarked in the terminal processes 

 of 0. radiata. In all published descriptions of 0. antiqua the stem 

 is said to be continued onwards and to geniculate, a fan-like system 

 originating at each geniculation. This may be so, but I have never 

 been able to convince myself that such is the fact : in all cases that 

 I have examined the second fan appears to arise at the termination 

 of two of the appendages of the first, the third from two of the 

 second, and so on. It is possible, however, that the ridges, which 

 I regard as representing two appendages, are the sides of a stem 

 crushed in along the middle ; but I can discover no feature by 

 which they are to be distinguished from ordinary appendages. 



