lET. 4 CAMBRIAN CONCHOSTRACA — ULRICH AND BASSLER 97 



similar instances of partial distortion were observed in the course of 

 these studies. Matthew's statement concerning a "narrow, oblique 

 tooth or ridge inside the shell at the hinge line" proves to be based on 

 a crumpling of the test at this point and not on a structural feature 

 of the hinge. The marking of the surface by "two diverging rows of 

 shallow impressions" and the "small round tubercles" seem both to 

 be somewhat fanciful interpretations of what are believed to be merely 

 accidental indentations of the inner and outer surfaces of the test by 

 grains of sand. 



The composition of the test is not the same as in true Lepiditta but 

 agrees essentially with that of the shell of Bradoria and Beyrichona. 

 Being convinced that the dorsal half of the type of L. sigillata has 

 been crushed almost out of existence, a comparison of the remaining 

 ventral half with corresponding parts of species of Bradoria and 

 Beyrichona brought out the fact that in at least one of the species of 

 I the latter genus, namely, Beyrichona planata, the lower half of the 

 valve corresponds exactly with the specimen under discussion. The 

 probability thus suggested may be satisfactorily tested by covering, 

 somewhat obliquely, the upper part of Figure 4 on Plate 6, and com- 

 paring the remaining portion with the enlarged photograph of L. 

 sigillata on Plate 7. In corroboration it remains to be said that 

 L. sigillata came from the same stratigraphic division, if not the same 

 layer, as B. planata. 



Occurrence. — Lower Cambrian (Hanfordian, division Cl63); Han- 

 ford Brook, New Brunswick. 



Genus FORDILLA Walcott 



Fordilla Walcott, Bull. U. S. Geol. Surv., No. 30, 1886, p. 123.— Miller 

 North Amer. Geol. and Pal., 1889, p. 480. 



Although closely resembling a pelecypod in outUne, the interesting 

 species upon which Fordilla is based has the calcareo-phosphatic 

 structure of genera here referred to the Limnadiidae. The type spe- 

 cies has been described in detail by various authors and we have noted 

 our idea of its relationships in the discussion of Lepiditta. 



Genotype. — Fordilla troyensis Barrande. Lower Cambrian. 



FORDILLA TROYENSIS Barrande 



Plate 4, Figures 14, 15 



Fordilla troyensis Barrande, Acephales: Ext. Syst. Sil. du Centre Boheme, 1881, 

 Expl. pi. 361.— Walcott, Bull, U. S. Geol. Surv., No. 30, 1886, p. 125, 

 pi. 11, figs. 3, 3o-c; Amer. Jour. Sci., ser. 3, vol. 34, 1887, p. 192.^Shaler 

 and FoERSTE, Bull. Mus. Comp. Zool., No. 16, 1888, p. 29, pi. 1, fig. 4.— 

 Lesley, Geol. Surv. Pa. Rept., p. 4, 1889, p. 251, 4 text figs. only. — Miller, 

 North Amer. Geol. and Pal., 1889, p. 480, text fig. 825.— Walcott, Tenth 

 Ann. Rept. U. S. Geol. Surv., 1890, p. 615, pi. 73, figs. 1?, 2, 2a-c. 



2607—31 7 



