82 The Irish Naturalist April, 



therefore, while the upper part formed an arch or tunnel into 

 which the mud flowed up from below, remaining as a mould 

 of each filament or rod ; while O. radiata simply decayed 

 away, leaving a depression, into which the next mud-layer 

 sank from above. 



The impressions, however, are often continuous through 

 several layers. There is no difficulty in accounting for this 

 in the case of Oldhamia antiqua. The author suggests that, 

 in the case of O. radiata the lowest impression is the original 

 dimple formed by the filament resting on the mud ; the 

 overlying and now sunken layers were deposited before the 

 filament decayed ; and, when it did so, they all bent down 

 into the hollow as it was vacated by the organic matter. 



The facts certainly seem at first opposed to any annelid- 

 theory of Oldhamia. If the markings were produced by 

 movements of tentacles, or of the body of a worm, round 

 about its burrow, these traces would probably not be identical 

 in successive layers. But maj^ we not accept Prof. Sollas's 

 suggestions gratefully, and yet see in the markings of O. 

 radiata a record of the ultimate positions of extended crowns 

 of tentacles, which at first resisted, and then decayed away as 

 he has supposed ? Were it not for the remarkable observation 

 of Prof. Joly, it would be tempting to see in O. antiqua similar 

 crowns of tentacles swept over sideways and killed off by a 

 rush of water bearing the mud that formed the succeeding 

 layer. The fan-like or tassel-like form would thus be ex- 

 plicable, as anyone may realise by experiments on the 

 appendages of an ordinary window- blind ; and the fact that 

 O. radiata occurs in one stratum, which would be, on this 

 theory, a quiet-water stratum, and O. antiqua in another, 

 would then seem natural enough. Prof. Joly's discovery, 

 however, points to a genuine specific difference between the 

 two ; and the regularity of arrangement in many specimens 

 of O. antiqua also opposes the above suggestion. 



The annelid-theory, however, deserves closer attention, 

 owing to modern researches in America. Mr. G. F. Matthew 1 

 has described from the Cambrian of St. John, New Brunswick, 

 a number of tracks and markings, which he attributes to 



1 ♦'Illustrations of the Fauna of the St. John Group, No. V." Tram. 

 Roy. Soc, Canada, Section iv., 1890, pp. 123-166, 



