FOSSIL FOOTPRINTS OF THE JURA-^TRIAS. 539 



Arachnichnus dehiscens E. Ilittlicock. 

 Arachiiirhiriis (Ifhisceiix E. Hitchcock, '58, p- 11". pi. -iO, fig. 12-13; pi. 38, fig. 2. 



Specific characters. Pes: tlivarication of lateral anterior digits, 150°. Length of 

 foot, .028 in.; breadth. .(llT m. Length of step, .070 to .114 m. Width of trackway, 

 .076 ni. 



Manns: divarication of lateral digits, 180°. Length of impression, .009 m. 

 Breadth, .013 ni. 



Tlie footprints are obscured by radiating sun cracks but their nearest affinity seems 

 to be with Palamopus. 



Tj^pe specimen, no. fi, of the Hitchcock cabinet, on shale from Turner's Falls, Massa- 

 chusetts (figured in E. Hitchcock, '65, pi. 17, fig. 2). 



Genus Triaenopus E. Hitchcock. (Anchor foot.) 

 Trlaciiapiis E. Hitchcock, '45b, p. 24. 



Generic characters. Author's description : " Quadrupedal, tetradactyloiis on both 

 fore and hind feet. Toes slender and long ; three directed forward with small divarica- 

 tion. Fourth toe coming out near the extremity of a long heel." 



This is a Weathersfield shale genus and, while very common, is extremely obscure as 

 to its true characters. It is nearly impossible to distinguish the fore and hind feet and 

 we may have another instance ' in which the successive tracks of two bipedal animals 

 appear as those of one quadruped. 



Triaenopus baileyanus E. Hitchcock. 



Triaeno2yus baileyanus E. Hitchcock, '45b, p. 24. 

 Triaenopus emmonsianus E. Hitchcock, '45b, p. 24. 



Trlaejiojnis lej^todactylus E. Hitchcock, '58, p. Ill, pi- 10, fig. 1-9; pi. 20, fig. 1-3; 

 pi. 4.5, fig. 8; pi. 52, fig. 1. 



Hitchcock here substituted the name T. leptodactyhis for the species whose pes was 

 formerly described as T. baileyanus, the manus as T. emmcjuslanus. The name T. bailey- 

 anus takes precedence. 



Type specimen, no. ||, of the Hitchcock cabinet, on red shale, from Weathersfield, 

 Connecticut. 



' Vide Plesioini.s, p. u21. 



