THE NATURAL HISTORY SURVEY. at BE 
ORDER TELEODESMACEA. 
‘‘Pelecypods with reticulate gills, the ventricle of the heart 
embracing the rectum; having the lobes of the mantle generally 
more or less connected and usually possessing developed 
siphons; the adductors practically equal; the shell structure 
cellulo-crystalline (porcellanous) or obscurely prismatic, never 
nacreous; the dorsal area, if present, always prosodetic or di- 
vided into lunule and escutcheon; ligament opisthodetic, with 
or without separate resilium; Saioin a lithodesma, rarely with 
external accessory shelly pieces; armature of the hinge charac- 
terized by the separation of the hinge teeth into distinct cardi- 
nals and laterals, the posterior laterals when present are be- 
hind the ligament; the animals active or nestling, sometimes 
sessile, but rarely sedentary burrowers, rarely inequivalve, usu- 
ally possessing a hinge plate and a pallial sinus. The sexes 
usually separate.” (Dall.) 
Superfamily Cyrenacea. 
““Cypricardians which have become specialized for fresh or 
brackish water conditions, and, as usual in such cases, have de- 
veloped great variability of character.” (Dall.) 
FAMILY SPHARIIDZ.* 
‘“‘Anatomy much asin Cyrenide, except that the siphons are 
separate and plain, the branchial sometimes not complete below; 
the foot prolonged ventrally, narrow, grooved, byssiferous when 
young; moneecious, the nepionic young incubated in a mar- 
supium formed by the inner limb of the ctenidia; confined to 
fresh water. 
‘Shell asin Cyrenide, but small, with a feeble, short ligament, 
a simple pallial line, no hinge plate; the cardinal teeth (usually 
two in each valve) variable, very thin, often nearly parallel to 
the hinge-margin or defective in part of the series; the laterals 
in Cyrenide distinct; the nepionic stage of the shell often con- 
spicuous on the beaks.”’ (Dall.) 
Genus SPH/AERIUM alge iy & Oe 
Spherium Scoroui, Introduct. ad Hist. Nat., p. 897, 1777. 
Cyclas BruGuterE, Encyc. Méth.,, p. 301, 1792, 
“Shell; Thin, oval or suborbicular, inflated, covered by a 
greenish epidermis; cardinal teeth very small or rudimentary, 
*Dall, Trans. Wagn. Free Institute of Sci., Vol. III., pt. iii., p. 540. 
