74 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 78 



observed that the anterior edge of /. longula is less rounded and 

 more nearly rectangular with respect to the hinge line, the postero- 

 dorsal part of the outline more rounded, the posterior terminus 

 of the hinge ill-marked, the postventral extremity more prolonged, 

 and the angle of the longest axis of the carapace to the hinge line 

 wider. In the last respect /. longula agrees with /. pyriformis, 

 but the postdorsal angle is so much better developed in that species 

 that these two forms, despite the fact that they are nearly equal in 

 size, are not likely to be confused. A closer ally than either of the 

 former seems to be indicated in /. dermatoides , a New York species of 

 nearly the same age. Still the latter is easily distinguished by its more 

 sharply defined cardinal angles, less oblique form, and less narrowly 

 rounded posterior extremity. It is also a smaller form. Another 

 close relative is the new I. subereda, but the shorter hinge and more 

 erect habit of the latter are such striking differences that a glance 

 suffices in distinguishing them. The other remaining species referred 

 to Indiana are too obviously different to require comparison. 



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

 ford Brook, St. John County, New Brunswick. 



Holotype— Cat. No. 50558, U.S.N.M. 



INDIANA SUBERECTA, new species 



Plate 9, Figure 28 



Description.— C&T&Ymce slightly exceeding the average for the 

 genus in size, subelliptical in outline, truncated dorsally so that 

 when the hinge is placed horizontally the habit is more nearly erect 

 than in any other species; anterior side and hinge Une forming a 

 right angle, postdorsal angle obtuse but fairly distinct; ventral 

 margin very gently convex, the turn into the anterior edge rather 

 abrupt but not angular; posterior outline strongty convex in the 

 lower third, gently rounded in the middle third, and straight, with 

 a decided anterior inclination, in the upper third; between the 

 middle and upper thirds an obtuse angulation; hinge line short, 

 its length barely exceeding one-third of the greatest diameter of 

 carapace. Valves moderately convex, thickest in the posterior 

 half, with blunt, rimlike edges. Test black, with very minute, 

 crowded punctae, distinctly visible only under a high power of 

 magnification. 



Dimensions of type specimen, a right valve: Greatest diameter 

 (from antero-dorsal angle to postventral edge) 5.2 mm., length of 

 hinge line (slightly imperfect) about 2 mm., greatest width of pos- 

 terior half (measuring diagonally across valve) 3.2 mm., greatest 

 thickness about 1.1 mm. 



Remarks. — This species is distinguished- -by its comparatively erect 

 habit and short hinge. In both features it is approached by /. Ion- 



