ART. 9 NEW CAMBEIAN CRUSTACEA — EESSER 7 



laterally. In these cases the original convexity of the valvelike 

 portions of the carapace was reduced to almost paper thickness, the 

 originally high keel being more or less displaced from the normal 

 with attendant crowding together of the more dorsal and ventral por- 

 tions of the thin shell. In many other instances the two valves were 

 buried in more or less normal vertical position that resulted in the 

 two valves being pressed flat dorso-ventrally so that the dorsal line 

 traverses the middle of the fossil and the circumference or periphery 

 represents the original convexity of the conjoined valves. In such 

 cases, moreover, the normally converging ventral portions beyond 

 the keel were folded back underneath the diverging dorsal halves 

 of the valves. In such dorso-ventrally compressed specimens the 

 periphery usually is made by the serrated keel. 



Genotype. — Tuzoia retifera Walcott, 1912. 



StratigrafMc range. — Lower and Middle Cambrian. 



Geographic distribution. — Middle Cambrian in Manchuria and 

 British Columbia. Lower Cambrian, British Columbia, and Penn- 

 sylvania. 



TUZOIA RETIFERA Walcott 



riate 1, figures 1, 2 ; Plate 4, figure 3 



Tuzoia retifera Walcott, 1912, Smithsonian Misc. Coll., vol. 57, no. 6, p. 

 187, pi. 33, fig. 2. 



When Walcott first described this species in 1912 in the fourth pre- 

 liminary paper based on the 1910 and 1911 collections from the 

 Burgess shale quarry, he still had only the single specimen illus- 

 trated. Subsequently^, among more than a score of additional speci- 

 mens that appeared, some preserving the margins, certain ones ap- 

 parently represent this species and consequently a more complete 

 description may now be drawm. After careful scrutiny of the speci- 

 mens that have marginal spines and of the original type I have come 

 to the conclusion that in the latter the marginal spines have been 

 broken away and that it was not originally without them. 



The original description of the species relies exclusively on the il- 

 lustrations to present the characters of the animal. A formal 

 description even now will add nothing to what can be ascertained 

 from the present illustrations, particularly when these are studied in 

 conjunction with the foregoing generic outline. Several characters 

 may be emphasized by being specifically pointed out here. First, the 

 three posterior marginal spines, the central one in direct line with 

 the keel, may be noted. One or two smaller spines occur forward of 

 these. Along the margin, between both sets small spines or crenula- 

 tions mark the edge. None of the specimens available permit a defi- 

 nite determination of the presence or absence of spines along the 

 dorsal line where we usually find them in other species. 



