3 1 8 Ornithichnology. 



cavity made origiJially in the mud by the foot of the bird, has been 

 filled by a siliceous concretion^ differing; somewhat from the surround- 

 ing rock ; so that the' latter may be in a good measure detached, and 

 the former be left standing out very naturally from the rock — pre- 

 senting in fact a petrifaction of the entire foot. Such specimens, in- 

 deed, are not common, but I have obtained a few of them ; and by 

 means of gypsum casts, they may be multiplied to any extent. 

 O- tuberosus. Toes, three ; length of the foot, seven to eight 



F 



inches ; claw distinct in some specimens ; from one inch to one and a 

 half long ; tuberous swellings on the under side of the toes, quite dist 

 tinct. Heel very obvious. In one or two specimens in my possession, 

 the inner toe presents two prominences, and the middle one, three ; 

 those on the outer toe not being distinguishable* This corresponds, so 

 far as the inner and middle toes are concerned, with the number of 

 joints in the three toed living Grallae. 'Length of the step in this 

 species, twenty four to thirty three inches; occurs in Northampton, 

 east side of Mount Tom ; and I have seen a loose specimen of appa- 

 rently the same species, obtained in the vicinity of the Horse Race, 



m 



Gill. 



The most important difference between this and the last species, 

 consists in its smaller size. It mifjht, indeed, be thouo;ht that the O- 

 tuberosus is but the young of the O. gtganteus. But I have not no- 

 ticed intermediate specimens ; and besides, the middle toe of the for- 

 mer is longer in proportion to the others, than in the latter species ; 

 while the toes of the latter are a good deal more divaricate tban 

 those of the former- 



a. dubius. I have lately obtained from the quarry on the east 

 side of Mount Tom, in Northampton, a few specimens a good deal 

 worn, which have the general form of O. tuberosus^ but they are much 

 smaller, the foot being only four inches long, and the steps twelve 

 inches. Not improbably, it is a distinct species ; but at present 1 

 shall regard it as made by the young of O- tuberosus. 



Fig. 2, exhibits two rows of the tracks of O- tuberosus^ pointing 

 in opposite directions ; the impressions at one extremity interfering 

 with one another. The length of the foot in the right hand row, as 

 i«rell as of the three insulated tracks, near the upper left hand comer 

 of the figure, is eight inches, and the length of the step is twenty 

 eight inches ; but the foot of the left hand row is scarcely seven 

 inches long, and the step is twenty four inches. The feet of dif- 

 ferent species, and sometimes of different genera of living birds, differ 



