ART 4 CAMBRIAN CONCHOSTRACA — ULRICH AND BASSLER 63 



Valve semielliptical with anterior and posterior ends elevated into 

 prominent marginal ridges of about equal length, not meeting along 

 the ventral side. These ridges are separated by a depressed flat 

 surface which bears a low ridge near its middle, extending nearly at 

 right angles to the hinge line near which it ends in a low inconspicuous 

 tubercle. 



Occurrence. — Lower Cambrian (Hanfordian, division Cl6l); Han- 

 ford Brook, St. Martins, New Brunswick. 



mPPONICHARION CAVATUM Matthew 



Plate 7, Figure 32 



Hipponicharion cavatum Matthew, Trans. Royal Soc. Canada, vol. 11, sec. 4, 

 1894. p. 99, pi. 17, figs. 3a, h; Trans. New York Acad. Sci., vol. 14, 1895, p. 

 133, pi. 7, figs. 2a, b. 



As shown by the illustration H. cavatum differs from the genotype 

 H. eos in that the depressed surface between the marginal ridges is 

 strongly concave instead of flat. Both the marginal ridges and the 

 median one are narrower and higher and the latter is longer and turns 

 at its lower end. 



Occurrence. — Lower Cambrian (Hanfordian, division Cl6l, Cl63); 

 Hanford Brook, New Brunswick. 



mPPONICHARION MINUS Matthew 



Plate 7, Figure 30; Plate 2, Figures 14-16 



Hipponicharion minus Matthew, Trans. Royal Soc. Canada, vol. 11, sec. 4, 

 1894, p. 99, pi. 17, figs. 4a, b; Trans. New York Acad. Sci., vol. 14, 1895, p. 

 133, pi. 7, figs. 3a, b. 



This species is quite similar to H. cavatum, although smaller, and 

 differs in that the lateral ridges are low and almost join at the middle 

 of the ventral edge. The median ridge is shorter and nearer the end 

 of the valve. 



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

 ford Brook, New Brunswick. 



Plesioty pes. —Cat. No. 50552, U.S.N.M. 



fflPPONICHARION MATTHEWI Wiman 



Plate 2, Figures 17-20 



Hipponicharion matthewi Wiman, Bull. Geol. Inst. Upsala, vol. 6, pt. 1, 1902, 

 p. 49, pi. 1, figs. 40-44. 



As indicated in our generic notes, H. matthewi is related to the type 

 of the genus, but differs conspicuously in that the gap between the 

 marginal ridges along the ventral border is closed. It, therefore, 

 belongs to the H. confluens section of the genus, differing, however, in 

 that the dorsal ridge is at right angles to the margin, as in the typical 

 section, instead of parallel as in //. confluens. 



Occurrence .—Lower (Middle?) Cambrian; Glauconite sandstone! 

 Eggegrund, Sweden. 



