sp]r.T:Kir:\r. 1223 



A':il(I(' iiitlato ; latere postico inagis produclo, subatteiuialo, aiiguste 

 triiiK-ato. 



Hah. Tenasseriiii, 



The diiiiensioria of a specimen in the British Museum ai'e: — 



Long. 14, lat, 17, diain. 11 mm. 



A pale, uniform greenish-yellow shell ornamented with distant, 

 concentric riblets ; somewhat elongately ovate and considerably 

 intlated, especially remarkable for its thin texture. 



Sabfamily SPH.^RIIN.E. 



Shell small, ovate or trigonal, lateral and cardinal teeth more 

 or less developed, ligament external ; [jallial line entire. 

 Diatiibution. World-wide. 



Genus SPH^RIUM. 



Sphcerium, Scopoli, J777 : Scopoli, liitroduct. p. .397. 



Chama, d'Argenville, Hist. Nat. Lithol. Conch vl. no. 9, 1742, 



pp. (368, t!74, pi. 31. 

 Tellma, LinnjBus ; Linn. Syst. Nat. 10th ed. i, 17."8, p. 678. 

 Cardium, JJaCosia, Brit. Conch. 1778, p. 173, pi. 13, tig. 2. 

 Cyclas, Briiguiere, Encycl. M^th. 1792, pi. 301. 

 JS'ux, llumpbrey, Miis. Calonn. 1797, p. 59. 

 Musculium, Link, Coll. Univ. Best., pt. 3, 1807, p. 151. 

 Cornea, Megerle, Mag. Gesell. Naturf. Bt-rliu, v, 1811, p. 5(5. 

 Conieocyclds, Ferussac, Diet. Sci. Nat. xii, 1818, p. 277. 

 Amesuda, llaHneeque, Ann. Gen. Sci. Phys. et Nat. v, 1820, p. 310. 

 Ci/cladite^, Kriiger, Gesdi. Urwelt. ii, 1823, p. 409. 

 Pisidium, Verany, Descris. Geno\a, ii, 1840. 



Type, Sphcerium corneum, Linn. ; Europe, 



Range. World-wide. 



Shell thin, ovate, convex, subequdateral, covered witli a fine 

 periostracum, smooth or concentrically striate; umbones lightly 

 anteriorly inclineil ; anterior side rather shorter than the 

 posterior; margins of the valves simple; cardinal margins 

 thin; cardinal teeth small, that in the right valve often bifitl. 

 fitting between two oblique teeth in the left ; both anterior and 

 posterior lateral teeth compressed, divergent, somewhat pro- 

 jecting, lamelliform double in the right valve, single in the left ; 

 ligament external, weak, scarcely apparent ; palhal line entire. 



Animal having the edge of the mantle smooth ; foot tongue, 

 capable of considerable extension ; siphons moderately long, 

 united at their base, separated at the end ; the branchial siphon 

 somewhat the longer and broader ; siphonal orifices simple ; 

 palpes triangular, lanceolate; gills unequal, the outer the shorter 



