CAMBRIAN FOSSILS. 463 



pass into the rather broad frontal limb, which slopes directly downward to 

 the frontal margin, without any frontal groove or rim. The palpebral lobes 

 are situated opposite a point about two-thirds the distance from the pos- 

 terior to the anterior margin of the glabella. 



Formation and locality: Middle Cambrian, Gallatin limestone, Crow- 

 foot section, Gallatin Range, Yellowstone National Park. 



Arioxellus sp. undet. 

 PI. LXV, fig. 2. 



Only the central portion of the head of this species is known. It is so 

 distinct a type that I do 'not hesitate to refer it to the genus Arionellus. The 

 glabella is elongate, subcorneal; the glabella furrows are indicated by very 

 slight depressions, and the occipital furrow is almost obliterated. Fixed 

 cheeks as broad as the glabella and merging into the broad, rounded, 

 anterior frontal limb. The palpebral lobes are broken away and there 

 does not appear to be any frontal rim, the gently rounded slope from the 

 glabella to the margin being unbroken. The specimen strongly recalls 

 specimens of Arionellus from the Paradoxides zone of Newfoundland. 



Formation and locality: Middle Cambrian, Flathead formation, north 

 side of Soda Butte Creek, below saddle on ridge between Pebble and Soda 

 Butte creeks, Yellowstone National Park. 



LIOSTRACUS Angelin. 



LlOSTRACUS PARVUS 11. Sp. 



PI. LXV, fig. G. 



This form is represented by the central portions of three small heads. 

 The glabella is a little longer than broad; sides subparallel, broadly 

 truncated in front; three pairs of small glabella furrows are slightty indi- 

 cated; occipital furrow narrow and slightly impressed; occipital ring narrow 

 at the sides, broader at the center, and provided with a short occipital spine. 

 Free cheeks broad, convex, and separated from the glabella by a well- 

 defined dorsal furrow; anteriorly they merge into the narrow frontal rim; 

 ocular ridges narrow, passing almost directly outward from a point opposite 

 the anterior pair of glabella furrows to the anterior end of the .small, 

 narrow palpebral lobe; anterior rim nearly flat and distinguished from the 



