Page:Proceedings of the United States National Museum, Volume 76.djvu/134

6 Tuzoia when first described was referred to the Leptostraca, and subsequent studies have confirmed this position.

Henriksen (p. 11) suggests that Anomalocaris belongs to the same group and that it may be the body of Tuzoia or Carnarvonia. Walcott associated several phyllopod carapaces, which have since been referred to Hymenocaris and Isoxys, with Anomalocaris prior to the discovery of the numerous entire specimens of Hymenocaris in the Burgess shale. In support of Henriksen's idea that Anomalocaris may be the body of Tozoia it may be stated that three of the four localities yielding Tuzoia have thus far also furnished Anomalocaris and that the latter has been found independently only on Mount Stephen.


 * Tuzoia, 1912, Smithsonian Misc. Coll., vol. 57, no. 6, p. 187.
 * Tuzoia, 1928, Vidensk. Medd. fra Dansk naturh. Fören., vol. 86, p. 16.

Large phyllopod with carapace consisting of two convex valvelike portions. Shell thin, and lateral portions semi-oval, narrowed anteriorly, probably curved evenly downward from the dorsal line; each valve increasing in convexity from the edges toward the keel that extends almost the full length of the shell in an approximately central position; posterior margin usually has several large spines; smaller spines may edge all but the extreme anterior portion of the margin; strong spines along the dorsal line in many species; also on the central keel in some species, sometimes their broad bases unite to form a scalloped frill. Surface usually reticulate; the meshes on the keel and near the dorsal line usually smaller and more crowded than on other parts of the shell. No external eyes or muscle scars observed.

Comparisons.—Comparing Tuzoia with Protocaris we notice that the shape of the valves, their relative size and the presence of a keel make the two forms look much alike. However, Protocaris lacks the reticulations and marginal spines which are persistent features of Tuzoia and thus offers an easily applied means of distinguishing them. If Anomalocaris is actually the abdominal portion of Tuzoia considerable differences of body structure exist. Both specimens of Protocaris thus far obtained retain the soft body, whereas none of the numerous Tuzoia specimens do, which in itself points to a difference of structure.

Attitude of valves in burial.—Some of the specimens were entombed in such a position that both valves were flattened together