PISIDIUM. 59 



43. Spltaeriuiu forinosuiu, Meek and Hayden. — " Shell small, 

 oval, oblique, scarcely ventricose ; cardinal margin straight ; buccal end 

 rounded ; anal extremity obliquely truncate ; basal margin semielliptical 

 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, 0.17 ; Lat. 0.08 ; Diam. 0.14 inches. 

 Hah. Three miles above Fort Union, Nebraska, United States of America. 

 Tertiary formation. (Cabinet of Smithsonian Institution.) 



Cyclas formosa, Meek and Haydex, Proc. Acad. Nat. Sci. Phila. 



1856, 115. 

 Cyclas fragilis.^ Meek and Hayden, loc. sub. cit. 1856, 115. 

 Sphaerium formosum, Meek and Hayden, ib. May, 1860, 185. 



44. Spliaerium. subellipticuiu. Meek and Hayden. — "Shell 

 small, elliptical-ovate, somewhat ventricose, thin and fragile ; posterior 

 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. 0.24; Lat. 0.14 inches. 

 Hab. Three miles above Fort Union, Nebraska, United States of America. 

 Tertiary formation. (Cabinet of Smithsonian Institution.) 



Cyclas subelliptica, Meek and Hayden, Proc. Acad. Nat. Sci. Phila. 



1856, 115. 

 Sphserium subellipticum, Meek and Hayden, ib. May, 1860, 185. 



" 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, especially from the examination of muti- 

 lated 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. 



PISIDIUItt, Pfeiffek.i 



Pectunculus, List. 1685. — 3Iusculus, Gadlt. 1742. — Tellina, Mullek, 



1774. — Sphieriim, Scop. 1777. — Cardium, Poli, 1191.— Cyclas, 



Lamk. 1818. — Pera, Eugl esia,CoTdula, Leach, 1820. — Pkyseinoda, 



Raf. 1820. — Pisidium, Pf. 1821. — GalUhja, Da Costa, 1839.— 



Pisum, Gray (non Megekle), 1847. — Musculinm, Gkay (non 



Link), 1851. 



Animal elongate-oval, compressed laterally ; lobes of the 



mantle without tentacles, united posteriorly into a single, short 



' Pfeiflfer, Deiitsch. moll. 1821. 



