NO. 7 CAMBRO-ORDOVICIAN FOSSILS 23 1 



During the season of 191 1 Mr. L. D. Burling examined the eastern 

 side of the Van Home Range southwest of Otto Creek, west-north- 

 west of Field, and found on the west side of the amphitheater about 

 4 miles southwest of the mouth of Otto Creek, in the shales of the 

 Goodsir formation and within two hundred feet of the Ottertail 

 limestone, three species of fossils, two of which, Lingulella moos- 

 ensis and Ceratopyge canadensis, are identical with species found 

 at about the same horizon in the Ice River region by Mr. Allan. The 

 third species is probably identical with Lingulella ? allani of the same 

 formation. 



The broad question of the Cambro-Ordovician boundary in other 

 sections of North America is one that is still in process of adjustment 

 owing to the absence of detailed information as to the boundaries 

 between formations and the character of the faunas in the formations. 



In the monograph of the Cambrian Brachiopoda,' now in press, 

 several formations have been included in the Cambrian or in "passage 

 beds " between the Cambrian and Ordovician that will ultimately be 

 classified with the Ordovician, or, as in the case of the Missouri sec- 

 tion " of the Mississippi region, placed in a terrane between the Cam- 

 brian and Ordovician. 



OBOLUS MOLLISONENSIS, new species 

 Plate 35, figs. 10-12 



In external form this shell is similar to Oboliis (Broggeria) sal- 

 tcri ' c^f the Upper Cambrian and Lower Ordovician of northwestern 

 Europe. It dififers in having the area and vascular markings of 

 Obolus instead of the very characteristic interiors of O. (B.) salteri. 



The surface is marked by fine, irregular, concentric lines and 

 striae of growth, and may be slightly roughened by the irregular 

 lines forming a minute, very irregular pseudo-reticulated surface. 



The largest ventral valve has a length of 7 mm. and a width of 

 about 8 mm. The average size is about 5 mm. in length. 



Formation and locality. — Lower Ordovician : Goodsir formation 

 (lower part), west side of Moose Creek Valley on east slope of the 

 north ridge of Mount Mollison, elevation 6550 feet, about 10 miles 

 in an air line southeast of Leanchoil on the Canadian Pacific Rail- 

 way, British Columbia. 



Collection, J. A. Allan. 



^ Monogr. U. S. Geol. Survey, Vol. 51, 1912. [In press.] 

 ^ Ulrich, Bull. Geol. Soc. America, 191 1, Vol. 22, pi. 27. 

 'Cambrian Brachiopoda, Monogr. U. S. Geol. Survey, Vol. 51, 1912, i)l. 

 13, figs. I, la-n ; pi. 15, figs. 4, 4a-d ; and p. 424. (In press.) 



