46 F 
EKWAN RIVER 
that they should rather be referred to Meristella or Reticularia. They 
seem to differ from Reticularia septentrional is in their uniformly, 
transversely and broadly sube'.liptical contour, and in the more 
depressed umbo of the ventral valve of each. 
MOLLUBCA. 
PELECYPODA. 
Ambonychia vndnlata (Whitfield). 
LcptotlnmuK uiululutu.'i, 'Whitfield. Ann. Rei>. (leol. Snrv. Wiscons. for 1877, 
p. 81 : and (1880) irtnil. Wiscons., vol. iv p. 29.3, pi. .xviii, figs. 1 and 2. 
Ekwaii river: portage road at falls, an imperfect left valve; and 
foot of portage road, a nearly perfect and very convex right valve. 
B >th of these specimens are marked with “ strong regularly rounded 
concentric undulations.” Mr. E. O, Ulrich, who has kindly examined 
the five specimens of pclecypoda collected by Mr. Dowling, and to 
whom the writer i.s indebted for some critical sugge.stions in regard to 
them, thinks that Leptodomus undulalns is an Ambonyrhia allied to 
A. planistriata, Hall, and that the former had fine surface radii. 
Ambonychia seplentrionalis, sp. nov. 
Shell obliquely and acuminately subovate or subrViomboidal, very 
inequilateral, rather strongly convex, most prominent in the umbonal 
region of each valve. Anterior side very .short, abruptly truncated, 
or rather intlected, and flattened ; po.sterior side a little longer, broadly 
rounded at its extremity an<l forming a subangular junction with the 
hinge line above. Umbones prominent, tumid but rather narrow . 
beaks incurved, anterior, and almost if not quite terminal ; hinge line 
straight behind the beaks, equal to about two thirds of the greatest 
length of the valves beneath. 
Surface marked with a few faint and obscure concentric undulations 
and lines of crowtli, also by extremely minute radiating lines. Test 
very thin. 
Hinge dentition and muscular impre.ssions unknown. 
Ekwan river, [lortage road at falls: a cast of the interior of both 
valves, with putt of the test preserved. 
This shell is rather similar to the A. njinis of Ulrich from the ^Middle 
(ialena of Minnesota and Illinoi.s, both in its shape and surface mar- 
kings. But, in the former the posterior end is more broadly rounded 
and not .so much produced below, and the radiating rai.sed lines of the 
surface are much more minute. 
