INVERTEBRATE PALEONTOLOGY. 531 



semi-ovate, being more proininenl before than behind the middle: posterior 

 side Ionizer and narrower than the other, angular at the extremity below; 

 beaks located in advance of the middle, rather elevated, particularly that 

 of the right valve, which is higher than the other; posterior umbonal slopes 

 angular from the beaks to the posterior basal extremity: surface orna- 

 mented by a tew strong, very regular, elevated, concentric undulations, which 

 are somewhat loss than the spaces between on the right valve, and propor- 

 tionally larger on the left. 



Length. 0.33 inch ; height, 0.25 inch. 



The strong regular undulations, or concentric' costse, on this little shell, 

 give it a peculiar appearance, and at once distinguish it from either of the 

 foregoing. The distinctly angular character of the posterior umbonal slope 

 of its valves, particularly that of the left valve, and its trigonal general outline, 

 indicate affinities to the Wyoming species from near Point of Rocks, already 

 mentioned; but its distinct, regular, concentric costa: and smaller size 

 readily distinguish it. 1 was for some time in doubt whether it really 

 belonged to this genus; but a view of the hinge and interior of the worn 

 and macerated left valve represented by our figure 4, d, reveals enough of 

 its generic characters to leave little room for doubts in regard to its belonging 

 to this group. 



Locality and position. — Same as last. 



GASTEROPODA. 



PULMONATA. 



LIMN^EIDiE. 



Genus LIMNJEA, Lamarck. 



Synon.—Limnwa, Lamarck (1799), Prodr. d'nn Nouv. Class. Coq., — ; ami (1801) Syst. An., 91; also 

 (1822) Hist., VI, 2, 157.— Cnvier (1806), Ann. du Mus., VII, 185.— Stiebel (1815), Diss. 

 Inaug. Syst. Limnd Staijnalis auat.— Schnru. (1817), Essai, 199.— Feruss. (1821), Tab. 

 Syst., xxxiii.— Blalnv. (1825), Malac, 448.— Fleming (1828), Hist. Brit. An., 273.— Say 

 (1832), Am. Conch. (Binuey ed„ 60).— Fitziuger (1833), Syst. Verz., 113.— Beck ( 1837), 

 Ind., lln.— Suaiuson (18401, Malac, 183, 338.— Gray (1840), Turton's Man. (2d ed.), 230 

 and 231.— G. B. Sowerby, jr. (1-42), Conch. Man. (2d ed.), 174.— II. and A. Adams 

 (1855), Genera Recent Moll., II, 252.— Binuey (1865), Land and Fresh-water Sheila N. 

 Am.. 24 : and of numerous others (not of Poli, 1791 = Unio, Ac ). 



Linuiaius, Limncus, Limnca, Lymnwus, and Lymna-a, Auct. 



Galha, Schrauek (1803), Fauna Boic, III. 2, 2-5. 



Radii, Montf. (1810). Couch. Sy.^t., II. 266. — Blainv. (1825), Malac. 149 (subgenus under 



Limnaa).— Gray (1840), Turton's Man. (2d ed.), 232 (as a subgenus).— Bi \ (1865), 



Land and Fresh-water Shells X. Am.. 30 (as a subg°nn8 under ZAmnasa). 



