3/8 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 64 



Matthew describes two small specimens of the dorsal shield as 

 follows : ^ 



.... In the II mm. tests (one-tenth of the length of the adult) there are 

 tubercles on the thoracic rings for the attachment of spines; in one example 

 these spines are attached to back of the rings ; that of the occipital ring crosses 

 two joints of the thorax, and that on the last joint of the thorax crosses three 

 rings of the pygidium. In the adult all these spines have disappeared except 

 that the fifth joint is sometimes seen to have a short spine. In the young shields 

 the geniculation of the pleurae, and the relief of the rachis are more pronounced 

 than in the adult. 



In the II mm. test there are eight joints in the thorax and 10 in the pygidium, 

 and eight costre on the side lobes of the latter. At this age, then, the species 

 had the full number of joints in the thorax, but lacked two of the full number 

 in the pygidium. Tests of 22 mm. length had an additional joint in the pygi- 

 dium, and in tests 35 mm. long, the full number was attained. 



A difference from the adult is observable in the length of the eye lobe of the 

 young: in these the proportion between the length of the anterior extension of 

 the suture of the eye lobe, and of the posterior extension are respectively 1,1, 

 2; in the adult it is i,^, i, 2j^ or 3. This contraction of the eye lobe is in 

 accordance with what has been observed in other genera, e. g. Paradox ides. 



I find that the minute spine or tubercle is almost invariably crushed 

 and left in the matrix, so that all that remains is the small base on the 

 transversely lined or corrugated posterior part of the axial portion 

 of the thoracic segment. 



From Dr. Matthew's description of the spines on the ii mm. speci- 

 men, it may be that he had a young specimen of Neolenus serratiis or 

 Zacanthoides spinosns, which are very abundant in association with 

 O. klotsi. 



Formation and locality. — Middle Cambrian : ( 14s) Ogygopsis zone 

 of the Stephen formation ; about 2,300 feet (707 m.) above the Lower 

 Cambrian and 3,540 feet (1,089 ^■) below the Upper Cambrian ; at 

 the great " fossil bed " on the northwest slope of Mount Stephen ; 

 and (sSr) about 2,200 feet (676.9 m.) above the Lower Cambrian, 

 and 3,725 feet (1,146 m.) below the Upper Cambrian, in the lime- 

 stones forming 2 of the Stephen formation, in the amphitheater 

 between Mounts Stephen and Dennis, both localities above Field on 

 the Canadian Pacific Railway, British Columbia, Canada. 



Also (sse) Spence shale horizon of the Ute formation; about 100 

 feet (30.5 m.) above the Brigham quartzite, at the mouth of the first 

 small canyon south of Wasatch Canyon, east of Lakeview Ranch, 

 5 miles (8 km.) north of Brigham, Boxelder County, Utah. 



^ Trans. Roy. Soc. Canada, 2d ser.. Vol. 5, Sec. 4, 1899, p. 58. Specimens in 

 Museum of University of Toronto, Canada. 



