Page:Proceedings of the United States National Museum, Volume 76.djvu/136

8 Whether the imperfect specimen illustrated on Plate 4, Figure 3, really should be regarded as belonging to this species can not be decided with certainty because of its incompleteness, but a careful study of it indicates that it likely does.

Horizon and locality.—Middle Cambrian, Burgess shale; (loc. 35k) near field, British Columbia.

Comparing this species with T. retifera we first note that it is longer and narrower and that the reticulations of the keel appear to be more numerous and stronger. The posterior marginal spines are about the same in both species but the small spines are larger and more regular both in size and spacing than in the genotype. Those of intermediate size appear to be absent. This species also has several blunt spines along the dorsal line the extensions of which are not as long or slender as in T. retifera.

Horizon and locality.—Middle Cambrian, Burgess shale; (loc. 35k) near Field, British Columbia.

Holotype and paratype.—Cat. No. 80477, U.S.N.M.

This second new species determinable in the Burgess shale material on hand is represented by only three or four fragmentary specimens, yet its specific characters may readily be seen.

Since the general shape and character of the reticulations of this species do not differ materially from the same features in both of the foregoing species its right to specific rank rests on others. The most prominent of these is the possession of four instead of three posterior spines which are longer and slenderer than in the preceding species and they are followed anteriorly by perhaps twelve or more of intermediate size, widely and evenly spaced along the margin, ending with one situated forward of the keel. Between these large and intermediate spines the usual small ones occur, in this case being most like those in T. retifera. The spines along the dorsal line are also longer and more slender, and perhaps more numerous than in T. burgessensis.

Horizon and locality.—Middle Cambrian, Burgess shale; (loc. 35k) near Field, British Columbia.

Holotype and paratype.—Cat. No. 80478, U.S.N.M.