n: IGOD4 



I'KIM i : i v i i M i in i \. n . 

 ri vi t MIII i uiB. -. 

 it i) .V> uiin.: thIi-kiieM 0. W nun. 



Valves strongly convex. subqnadrate-. .,'ht. rather long; posterior 



dorsal angle strong, the anterior more obtuse or rounded; ends nearly equal in hight, 

 but the anterior margin i- more curred than the posterior, the latter being some- 

 what truncated above; sulcus a little in front of. or quite in the middle of the dorsal 

 half, deep, with a strong rounded swelling on each side; the posterior prominence 

 larger ami higher than the anterior one, but the latter usually somewhat better 

 defined by a forward .-wing of the lower part, of the sulcus; surface beneath the 

 sulcn- prominently convex, and sometimes 1 tearing several small tubercles; a wide 

 ri.in-ave border, defined in the ventral part by a thin ridge, extending parallel with 

 ami some distanre within the edge of the valves. This ridge I consider as the 

 remnant of a false border, like the one which is so strongly developed in I'.tluplicntii. 



At first 1 thought this -pecie- might be the same as /'. cim-inmitirnxis Miller sp., 

 but a more careful examination proved it distinct, though perhaps closely related. 

 In ti higher, the ventral outline being much more curved. 



Next, the sulcus is relatively shorter, while the border is not narrow and flat. Hut 

 the most important difference is the submarginal ridge which is distinguishable 

 even on casts of the interior of /'. (unwluln, but of which not a sign is to be seen on 

 Miller's specif-. In /'. >li<i>li><itn this ridge is much more strongly developed, forming 

 a false border from one dorsal angle to the other. This fact causes the surface of 

 the valve- to appear much less convex than it really is, though the greatest thick- 

 ness is a little less than in /'. lumiilula. Hut the sulcu< in the latter is much de< 

 and the tumidity of the surrounding parts greater than in the Trenton 



locality. Iii a thin bed of shall- l-lunk'inj.' t<> tin- luwer part cif th.- Hudson I 

 i. tlirv.- mi!.- north illey, Minnesota. 



I'lMMITlV i.IHHKKA. II. * 



ii \TE xi. 111. nus. n-m. 

 n: hitfht ".45 nun.: thic-kneMO.36 mm. 



Valves somewhat leperditoid in outline, with _'ht hinge line, the distance 



veen the dorsal angles about five-ninth- of the greatest length of the carapace; 

 ends rounded; valves rather strongly convex, gibbon- in the anterior half of the 

 dorsal region; thi- prominent part i- somewhat tlatt.'iied on the back, and inrlndi- 

 a short and rather shallow notch or .sulcus. In the .-pecimen- at hand the -urfac.- 

 slopes uniformly toward the edges and these seem to be simple and without a border; 



