26 SMITHSONIAN MISCEI.LAN KOUS C(JLLKCTIONS VOL. 53 



Formation and Locality. — Middle Cambrian : Spence shale of 

 the Ute formation, 2,755 feet (839.7 m. ) below the Upper Cambrian 

 in the Liberty Canyon section ; Spence Gulch, a ravine running up 

 into Danish Flat from Mill Canyon, about 15 miles (9.37 km.) west 

 of Montpelier and 5 miles (3.12 km.) w^est-southwest of Libert\-, 

 Bear Lake County. Idaho, U. S. A. 



Genus ZACANTHOIDES Walcott 

 ZACANTHOIDES IDAHOENSIS, new species 



Pi.ATR 3, Figures i-i i 



Dorsal shield large for a species of this genus, moderately convex, 

 longitudinally elliptical in outline. Cephalon semicircular in out- 

 line, one-third the length of the adult dorsal shield ; bordered bv a 

 rounded rim of medium width that is continued into strong, sharp 

 genal spines that extend backward about one-half the length of the 

 thorax ; the posterior border is narrow next to the glabella, from 

 where it widens out to the intergenal spine within the line of the 

 facial suture ; beyond the facial suture it curves forward and merges 

 into the lateral border at the base of the genal spine ; the posterior 

 intermarginal furrow is sharply defined, and occupies most of the 

 space between the border and the facial suture ; on the sides and 

 front of the cephalon the intermarginal furrow is narrow and 

 distinct. Cranidium with a large glabella, short, small antero-lateral 

 limbs, and elongate, slender postero-lateral limbs that have a short, 

 sharp, slender, intergenal spine extending outward and backward 

 from the outer posterior margin ; fixed cheeks scarcely more than 

 the inner sides of the large palpebral lobes and a small, subtriaugular 

 area in front of the latter ; postero-lateral limbs formed of the 

 marginal border and strong, intermarginal furrows ; a narrow 

 frontal limb extends across between the glabella and the interborder 

 furrow ; palpebral lobe about three-fifths the length of the cranidium 

 and bordered by a narrow, rounded rim that begins, posteriorly, 

 near the median axis opposite the occipital ring, and. curving out- 

 ward, forward, and then inward, terminates at the dorsal furrow 

 beside the glabella ; it is separated froni the body of the lobe by a 

 rounded, shallow furrow. Glabella elongate, subquadrilateral in 

 outline, moderately convex in front, sides nearly straight, broadly 

 rounded, and separated from the fixed cheeks and palpebral lobes 

 by a narrow, distinct furrow ; surface marked by a pair of posterior 

 furrows that extend obliquely inward, so as to outline two small 

 subtriaugular lobes, and two pairs of short, more transverse fur- 

 rows ; the anterior pair is nearly opposite the anterior end of the 



