22 PROF. W. C. WILLIAMSON ON SOME UNDESCRIBED 



to share Schimper^s belief in their vegetable origin, I see 

 no objection to retaining his name. So far as I am aware, 

 all the examples o£ Chrossochorda hitherto known have 

 been obtained from strata of much older age than the 

 Yoredale series. But, besides this difference of age, these 

 Carboniferous forms differ from all the older ones in pos- 

 sessing the line of tubercles along the summit of each of the 

 secondary ridges already referred to. These objects may 

 therefore be distinguished as Chrossochorda tuberculata. 



What animal produced the hollow tracks of which 

 these fossils are casts in relief, we have no means of 

 knowing. There is an obvious resemblance between them 

 and the tracks which Dr. Nathorst obtained by allowing 

 the Crustacean Corophium longicorne to walk and swim 

 over prepared mud"^. In several similar tracks figured by 

 Dr. Nathorst we find the line of footsteps terminating in 

 enlarged irregular depressions, corresponding to the bosses 

 seen in figs, ic? & 3. 



Plate I. fig. 4 represents a track of an entirely different 

 kind, from a quarry of Carboniferous flagstones near 

 Hawesf- I presume that in this case we have not the 

 cast, but the actual indented track of the animal that has 

 left its footsteps on the smooth sands. The length of the 

 stone is lyf inches. Each separate group of impressions 

 consists of four pairs of slightly curved indentations, each 

 octant occupying a square i^^^. of an inch from a to b, 

 i-| of an inch from c to d, and nearly --^V from e to / of 

 the accompanying lignograph. The markings suggest the 

 idea of having been made by four pairs of abdominal plates 

 rather than by crustacean limbs. The distances between 



* Om spar af nagra evertebrerade Djur m. m., och dei'as paleontologiska 

 betydelse, af A. G. Nathorst. Stockholm, 1881. Tail. i. figs. 1-2. 



t Mr. J. W. Davis says, "The footprinls are from a quarry of flagstones 

 and grey slates about a mile from Hawes, on the road to Muker. The 

 horizon is above the Hardrow Limestone." 



