278 prof, w. j. sollas on ichnium [May 1900J 



interesting to observe that the resemblance of 0. radiata to the 

 tracks of worms had not escaped the notice of Nathorst, who, 

 however, only discusses the similarity to reject it as a valid ex- 

 planation. The first objection of this author, that the markings of 

 Oklhamia are too vaguely defined for the track of a worm, will 

 scarcely be admitted by those who have had the advantage of 

 examining fairly good specimens. Prof. Nathorst has apparently 

 seen only those contained in the collections of Munich and Lund, 

 and that these are possibly not very good examples is suggested by 

 the remark that the ordinary illustrations of Oldhamia are some- 

 what imaginative. This is a reproach which the careful drawings 

 of a number of distinguished palaeontologists — Salter, Kinahan, 

 and Baily — scarcely deserve ; for my part I am inclined to think 

 i hat an impartial student who should compare the original specimens 

 with the corresponding figures would be led to pronounce the 

 Latter as unusually good and remarkably true to nature. One of 

 .-niter's representations of 0. antiqua is perhaps slightly diagram- 

 matic, but not ' fort idealisee,' while Roemer's diagram of 0. radiata, 

 m> far from being, as Nathorst remarks, ' plus conforme a la nature/ 

 is a mere travesty of the actual marking. Baily's later figures are 

 lot quite so exact as his earlier ones, owing to a tendency to pro- 

 ject into them hydrozoonal characters, which expresses itself in a 

 somewhat jagged outline given to the margin of one side of the rays. 

 The remaining objections of Nathorst are cited from Ecemer (13) 

 as follows : — The parts of the marking are disposed in a completely 

 vregular manner; there is no definite centre towards which the 

 rays converge ; the markings are not connected with any difference 

 in chemical composition of the rock-matrix ; and finally, Oldhamia 

 is not accompanied by any other organic remains. Nathorst adds 

 that certain specimens of the ' marlekor ' of Lapland present in the 

 interior a structure resembling Oldhamia, and suggestive of a 

 possible i mechanico-chemical ' origin, but he does not give either 

 descriptions or figures of this structure. 



While some of the arguments advanced by Ecemer may be 

 calculated to dispel a belief in Oldhamia as representing the actual 

 remains of an organism, they are by no means opposed to the view 

 that it has been formed by the movements of some burrowing 

 worm. The tracks of recent worms figured by Nathorst are not 

 more regular than Old/umiia-m&rkings ; they are not characterized 

 by a more definite centre, nor are they more sharply defined, 

 probably rather less. They are not associated with chemical 

 differences of the mud, nor need they be accompanied by obvious 

 evidence of the existence of contemporary organisms. Finally, it can- 

 not be conceded that Oldhamia is destitute of companions ; ordinary 

 worm-tracks, such as are made by the crawling of animals over a 

 muddy surface, are more commonly found along with Oldhamia than 

 not. Histioderma hibernicum, almost certainly a worm-burrow, is a 

 well-known associate, and there are others : such as PucJcsia Mae- 

 henry i (25), which, though of- doubtful systematic position, is in- 

 dubitably of organic origin. After this discussion, in which the 



