ART. 4 CAMBRIAN CONCHOSTRACA— ULRICH AND BASSLER 73 



tinct — whether as varieties or good species to be determined here- 

 after. In distinguishing them, after the great difference in size, it is 

 to be noted that the valves of /. jpyrifonnis are relatively wider in 

 front, the hinge is longer, and the postdorsal angle not so broad, while 

 the posterior margin turns downward more rapidly. In consequence 

 of these small peculiarities, the retral swing of the outline is less strik- 

 ing than it appears in /. secunda. 



In the figure of a left valve published by Matthew the angular form 

 of the postcardinal region is not so well brought out as in the right 

 valve represented by our new figure. Critically compared, a slight 

 difference in thickness of valves is noted between the New Brunswick 

 and New York specimens. The latter are less convex than the former 

 but the difference is due, in part at least, to compression. 



Dimensions: Greatest length (diagonally across the carapace) 6.8 

 mm., length of hinge 4.1 mm., greatest height 4.7 mm., thickness 

 of right valve 1.7 mm. 



Occurrence. — Lower Cambrian (Hanfordian, division C1631), Long 

 Island, Kings County, New Brunswick; Hanford Brook, St. John 

 County, New Brunswick. In Washington County, N. Y., the species 

 occurs in association with /. dermatoides and /. secunda, in lime- 

 stone correlated as Lower Cambrian by Doctor Walcott. 



Plesiohjpe.— Cat. No. 56470, U.S.N.M. 



INDIANA LONGULA, new species 



Plate 9, Figures 19-21 



Description. — Carapace larger than usual for the genus, obliquely 

 subehiptical, produced posteriorly, the postventral extremity nar- 

 rowly rounded; anterior end small, truncated vertically with respect 

 to the hinge line; hinge short, less than half the greatest diameter 

 of carapace; post-dorsal angle undefined, the anterior conspicuous 

 but rounded off. Other features apparently the same as in /. se- 

 cunda. 



Dimensions: Greatest length (measuring from the antero-dorsal 

 angle to the post ventral margin) 7.5 mm., length of hinge about 

 4 mm., width from middle of ventral side to the post dorsal edge 

 4.5 mm., thickness 3.5 mm. or more. 



Remarks. — But a single example of this species has been seen. 

 It retains both valves in nearly perfect condition. The edges of 

 the valves have all the appearance of overlapping along the ventral 

 side as in Leperditia, but this condition is most probably abnormal. 

 That it resulted from the valves being forced together is indicated 

 by the ragged edge of the overlapping (left) valve, as shown in our 

 figure. 



Except that the specimen is much larger, it bears a striking general 

 resemblance to /. secunda. On closer comparison, however, it is 



