NO. 10 CAMBRIAN FOSSILS, 4TH CONTRIBUTION RESSER 13 



Helcionella walcotti, n. sp. 



Stcnotheca riigosa Walcott (part), loth Ann. Rep. U. S. Geol. Surv., p. 617, 

 pi. 74, fig. le, 1891 [see H. rugosa]. 



This is the most common species in the Hudson valley. It has the 

 coarsest ribs, and differs further in that the ribs are angular while 

 in Other species they are rounded in contour. 



Lower Cambrian, Schodack; (loc. 33) North Greenwich, and 

 many other localities in New York. 



Holotype.—U.S.'HM. no. 17456. 



Helcionella curticei, n. sp. 



Stctwthcca rugosa Walcott (part), U. S. Geol. Surv. Bull. 30, p. 128, pi. 12, 

 fig. I, 1886; idem, loth Ann. Rep., p. 617, pi. 74, fig. i, i8gi [see H. 

 rugosa]. 



The holotype lies in the matrix, besides a good example of 

 H . rugosa, so that it is easy to compare the two. H. curticei, which 

 is named for the collector, is twice as high as II. rugosa, has a more 

 rounded elliptical outline and coarser ribbing. 



Lower Cambrian, Schodack; (loc. 27) Troy, New York. 



HoIotypc.^V. S.'N.M. no. 96473. 



Helcionella fordi, n. sp. 

 Stcnotheca rugosa Walcott (part), U. S. Geol. Surv. Bull. 30, p. 128, pi. 12, 

 fig. la, 1886; idem, loth Ann. Rep., p. 617, pi. 74, fig. la, 1891 [see H. 

 rugosa]. 



H. fordi has a much rounder elliptical outline than H. rugosa. 

 The rugosity is stronger than in H. curticei, from which H. fordi 

 further differs in greater relative height. 



Occurrence same as preceding. 



Holotype. — U.S.N.M. no. 96474. 



Helcionella tatei, n. sp. 



Stcnotheca rtigosa Tate, Trans. Roy. Soc. South Australia, vol. 15, p. 183, 

 pi. 2, fig. 4, 1892. 



This species is characterized by its wide base. The sides slope 

 evenly and the apex is overturned, but only near its tip. As shown 

 in the figure the ribs are angular, but they are not pronounced. There 

 are also vertical striations. 



Lower Cambrian ; Androssan, South Australia. 



Holotype. — Australia; plastotypes, U.S.N.M. no. 96475. 



