336 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 53 



ones. They have not been observed on all the intermediate segments, but this 

 may be owing to bad preservation or faulty observation, as it is probable that 

 they once existed. 



The teJson is long and styliform, and tapers rapidly at first and then decreas- 

 ingly. Its articulation with the last free segment is well shown in the specimen 

 from which pi. 30, fig. 12, was taken. Projecting from the posterior margin 

 of the axis of the fourteenth free segment, at about 1-5 of its width from each 

 side, are two small protuberances. Corresponding projections proceed forwards 

 from the hinge-line of the telson, and interlock with them on their outside. 

 Beyond them the anterior edge of the telson is continued in nearly the same line 

 with the hinge, so that the anterior angles of the telson appear to be overlapped 

 by the pleura of the last free segment. A "lock joint" is thus formed which 

 does not allow of the telson folding downward beyond a certain angle with the 

 plane nf the last segment. 



The most marked and to me important point of difference with 

 0. lapzvorthi is the much smaller eye. This is best seen by com- 

 paring fig. 12 with fig. I on pi. 39. The eye of O. retictdatns is like 

 that of 0. canadensis [pi. 38, figs. 4, 5, 6], and in both species we 

 find a tubercle between the posterior end of the eye lobe and the 

 glabella. 



Formation and Locality. — Lower Cambrian : argillaceous shale 

 interbedded in " Serpulite grit," a coarse quartzitic sandstone, north- 

 ern slope of Meal a' Ghubhais, 1,200-1,300 feet (366-396 m.) above 

 Loch Maree, 4 miles (6.4 km.) northwest of Kenlochewe in the west 

 of Ross-shire, Scotland. 



OLENELLUS THOMPSONI (Hall) 



Plate 34, Fig. 9; Plate 35, Figs. 1-7 



Olenus thompsoni Hall, 1859, Twelfth Ann. Rept. New York State Cab. 

 Nat. Hist, p. 59, fig. I, p. 60. (Described as a new species.) 



Olenus thompsoni Hall, 1859, Nat. Hist. New York, Paleontology, Vol. 

 3, pt. I, pp. 525-526, text figure, p. 526. (Copy of the preceding 

 reference.) 



Barrandia thompsoni Hall, i860, Thirteenth Ann. Rept. New York State 

 Cab. Nat. Hist., pp. 115-116, text figure, p. 116. (Described, beginning 

 with the sth paragraph under "Genus Barrandia.") 



Paradoxides asaphoides Emmons, i860. Manual of Geology, 2d ed., p. 87. 

 (Name used in legend of fig. 70, p. 87, see following reference.) 



Paradoxides macrocephalus Emmons, i860, Idem, p. 88, fig. 70. (In the 

 text reference on page 87 this figure is referred to as Paradoxides asa- 

 phoides; but from the figure there is little doubt that it was taken from 

 a specimen of O. thompsoni. In the first edition of the Manual of 

 Geology the figure is labeled Paradoxides brachycephalus. On page 

 280 there is a note on the stratigraphic position of the species.) 



