NO. 3 CAMBRIAN AND OZARKIAN TRILOBITES 95 



Housia canadensis is one of the species with a genal spine. The 

 •illustration of the head in figure ii, plate 22, is the cast of the under 

 side of the test. The striations shown on the frontal rim, which is 

 here less distinct than on the dorsal side, are possibly not impressed 

 on the upper surface. 



In several of the pygidia the border is broken away exposing the 

 striated doublure. The test of this trilobite apparently was smooth, 

 except possibly radiating irregular lines on the free cheek, a feature 

 found in another better preserved species. 



H. canadensis differs from H. varro in the presence of the genal 

 spine, which results in a less cnxular outline for the free cheeks. 

 The facial suture diverges a little more. The pygidium oi H. cana- 

 densis has more clearly marked axial and pleural furrows. The rim 

 is also relatively wider. 



Formation and locality. — Upper Cambrian, Goodsir formation. Ice 

 River Valley about six to eight miles (9.7 to 12.9 km.) southeast 

 of I.eanchoil Station; Moose Creek; and Mount Goodsir, British 

 Columbia. 



HOUSIA VARRO (Walcott) 



Plate 18, figs. 4-8 



Dolichometopus (Housia) varro Walcott, 1916, Smithsonian Misc. Coll., 



Vol. 64, No. 5, p. 374, pi. 65, figs. I, la-e. 

 Housia varro Walcott, 1924, Smithsonian Misc. Coll., Vol. 75, No. 2, p. 57, 



pi. 12, fig. 4. 



The original description, together with the generic diagnosis, gives 

 the character of this species. 



Formation and locality. — Upper Cambrian: (30y) Orr formation. 

 Orr Ridge, south of Marjum Pass, House Range, Utah. 



Genus IDAHOIA Walcott 



Idahoia Walcott, 1924, Smithsonian Misc. Coll., Vol. 75, No. 2, p. 58. 



Description. — The genus Idahoia is characterized by the unusual 

 development of the frontal limb. The glabella occupies only about 

 half the length of the cranidium and has no glabellar nor occipital 

 furrow. The broad occipital segment bears a strong occipital spine 

 that is nearly as long as the glabella. Dorsal furrow well-marked 

 and transverse in front of the glabella, which tapers slightly. The 

 facial sutures delimit long and narrow postero-lateral limbs and 

 diverge rapidly in front of the eyes and are entirely intramarginal. 

 The frontal limb is composed of three wide parts. On the cranidium 



