26 PROF. W. C. WILLIAMSON ON SOME UNDESCRIBED 



other detailed illustrations of drainage-lines contributing 

 towards the formation of pseudo-organic structures'^, still 

 less to the combination of drainage-lines and ripple-marks 

 in producing analogous results ; yet the literature of the 

 subject of tracks and pseudo -vegetable forms has now 

 become a very copious one. 



In his extremely valuable memoir "On some Tracks 

 of Invertebrate Animals &c., and their Palseontological 

 Import^''t, Dr. Nathorst has published a bibliography of 

 the subject treated in his memoir, containing no less than 

 130 references to writers who have dealt with various 

 aspects of the subject between the years 1823 and 1881 

 inclusive. Many of these writers have regarded the objects 

 to which they have referred as the tracks or footsteps of 

 various invertebrates left upon the sandy or muddy shores 

 which they frequented; but a large proportion of the 

 authors have referred these objects to the vegetable 

 kingdom, especially to the Fucoidal section of it. The 

 extent to which this has been done is shown in the pages 

 of Schimper^s ^ Paleontologie Vegetale/ where a large 

 number of genera, and a still larger one of species, have 

 been created out of extremely vague and indefinite objects. 

 More recently the Marquis de Saporta has published his 

 volume, entitled 'L^Evolution du Regne Vegetale ^ (Paris, 

 188 1), in which he adopts freely the conclusions of 

 Schimper, and recognizes in these doubtful objects various 

 definite forms of marine Algge. 



The Marquis de Saporta first replied to the memoir of 

 M. Nathorst in a volume entitled ' Les Organismes pro- 

 blematiqucs des anciennes Mers/ 1882, and two days ago 

 I received from him a second volume, entitled 'A propos 



* My ignorance of the Swedish language has led me to overlook the fact 

 that Dr. Nathorst figures an example of this kind on p. 21 of his memoir 

 supplied to him from Gothland by Professor Lindstrom (July 25th, 1885). 



t Om spar af nagra evertebrerade Djur m. m., och deras paleontologiska 

 betvdelse, af A. Gr. Nathorst. Stockholm, 1881. 



