14 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 'J'J 



and while none of the imprints have more than three toes registered, 

 the close agreement in foot proportions, width of trackway, and 

 length of stride all point to its affinities with the above mentioned 

 genus and species. 



As originally determined by Lull, Laoporus has four toes on the 

 manus and five on the pes, this being fully substantiated by the 

 paratype (No. 8422, U. S. N. M.) upon which the genus is par- 

 tially based, and which has been of the greatest assistance in arriv- 

 ing at a proper identification of the recently acquired material. The 

 shallowness of the prints on slab No. 11,148, U. S. National Museum, 

 largely explains the absence of the missing toe impressions, and that 

 there were other toes is evidenced by the lateral projection of the 

 foot mass, entirely sufficient to have carried the proper number of 

 additional digits. 



Fig. 8. — Limnopus vagus Marsh. Outline of fore and hind foot- 

 prints of left side. Natural size. (Afte^ Marsh.) 



A second slab (No. 11,122, U. S. N. M.) from the same level 

 has on its surface a considerable number of footprints (see pi. 6) 

 which also seem to belong to this genus and species. While these 

 do not form a well-defined trackway, the clearness of many of the 

 imprints contributes to a much better understanding of the detailed 

 structure of the feet than has hitherto been obtained. All of the 

 better impressed tracks are slightly larger than those of the type 

 and other specimens, as may be seen by reference to the table of 

 comparative measurements (p. 16), but those of the forefoot are 

 almost identical in all other features with the paratype. 



A study of the paratype in combination with these new specimens 

 gives such a different conception of the plan of the feet from those 

 depicted by Lull as to require a new drawing which is shown in 

 figure 9. The manus, as clearly shown in the paratype, has only four 

 digits, but they are distinctly separated at their bases, with a short, 

 slender first digit and a slightly longer but divergent fourth. Digits 



