19 



Long. 0-38 ; lat. 0-32 ; diam. 0-08 inch. 



Hob. Near the mouth of Grand River, on the Upper Missouri, Nebraska, 

 U. S. of America. Tertiary formation. 



37. Sph. formosum, Meek and Hayden. 



Cyclas formosa, M. & H., Ac. N. S. Phil., Proc., 115, 1856. 

 " fragllis, M. & H., loc. sub. cit., 115, 1856. 



Shell small, oval, oblique, scarcely ventricose ; cardinal margin straight ; 

 buccal end rounded ; anal extremity obliquely truncate ; basal margin semi- 

 elliptical or broadly rounded ; beaks obtuse, tumid, rising somewhat above 

 the hinge, nearly touching, placed a little in advance of the middle ; surface 

 ornamented by very fine, regular, distinct, concentric wrinkles. 



Long. -17 ; lat. -08 ; diam. -14 inch. 



Hob. Three miles above Fort Union, Nebraska, U. S of America. Ter- 

 tiary Formation. 



38. Sph. subellipticum, Meek and Hayden. 



Cyclas subelliptica, M. & H., Ac. N. S. Phil. Proc., 115, 1856. 



Shell small, elliptical-ovate, somewhat ventricose, thin and fragile ; pos- 

 terior end narrower than the anterior, both narrowly rounded ; base semi- 

 elliptical or semiovate ; cardinal border apparently rounding gradually to 

 both extremities ; beaks not much elevated, pointed, incurved, not oblique, 

 located near the middle ; surface indistinctly marked with lines of growth. 



Long. -24 ; lat. -14 inch. 



Hab. Three miles above Fort Union, Nebraska, U. S. of America. Ter- 

 tiary Formation. 



' ' The beaks are so near the middle, and curved so nearly at right angles to 

 the longitudinal diameter of the shell, that it is not easy to determine, espe- 

 cially from the examination of mutilated specimens, which is the posterior or 

 which the anterior end. As we have only seen imperfect specimens, we are 

 not sure the surface markings are indistinct on unworn shells." M. & H. 



The following shells, known under the name of Cyclas, must be excluded 

 from the list of American species of Sphaerium, in some cases because they 

 have been improperly placed in this genus, and in others, because no descrip- 

 tion has been published : 



Cyclas a e q u a 1 i s, Rafmesque, is Pisid. Virginicum. 

 al t il i s, Anthony, is Pisid. compressuin. 

 Americana, Christof. and Jan. Undescribed. 

 Carolinian a, Bos., is Cyrena Caroliniensis. 

 C h i 1 e n s i s, D'Orbigny, is Pisid. Chilense. 

 clandestina, Da Costa, is a marine shell, 

 d e n s a t a, D'Orbigny, (fossil,) is Cyrena densata. 

 d u b i a, Say, is Pisid. Virginicum. 

 f 1 u v i a t i 1 i s, Bosc, is a Corbicula. 

 Fontaineii, D'Orbigny, is Cyrena Fontaineii. 

 hammalis, Rafin., is a Corbicula. 

 1 i m o s a, D'Orbigny, is Corbicula limosa. 

 m aritima, D'Orbigny, is Cyrena Cubensis. 

 minor, C. B. Adams, is Pisid. abditum. 

 nitida, Adams & Mighl., is Pisid. Adamsi. 

 o v a t a, Lewis. Undescribed. 

 Paranensis, D'Orbigny, is Corbicula Paranensis. 

 pygmea, C. B. Adams, is Pisid. Jamaicense. 

 variegata, D'Orbigny, is Corbicula limosa. 

 V i r g i n i c a, Ferussac, is Pisid. Virginicum. 



