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TAXYSIPHOy. 201
" The specimens received in spirits show that the mantle is
closed at the basal edge, presenting narrow openings at either
extremity for the passage of the siphonal sheath and foot. The
suture is nearly straight, scarcely undulate. The foot is thick
and cartilaginous, broad, and with a pit or depression at the
anterior end, and laterallj'' hamate, or bent like the crook of a
walking-stick, the point being towards the hinge-side and thes
hinder edge straight, not concave."
324. Tanysiphon rivalis, Beiison.
Tamjsq)hon rivalis, Benson, A. M. N. H. ser. 3, i, 1858, p. 408,
pi. 12 B, figs. 1-3 ; H. & T., 0. I. 1876, p. 47, pi. Il6,
figs. 1 & 4.
Original description:—Testa tenui, transverse oblonga, antiee
breviori obtusa, postice longiori, angustiori, extus tenuiter striata
et irregulariter remote rugosa, epidermide pallide cornea; natibus
decorticatis latis prominentibus, umbonibus obtusis; valvis male
congruentibus, per spatium breve cardinale et ventrale solum
taetum exhibentibus ; humero umbonali antico breviter compressiusculo;
area interiori cserulescenti-alba.
Long. 11, lat. 21, diam. 9 mm.
Hah. Streams in the neighbourhood of Calentta.
Family CYRENID^.
Subfamily CYRENINiE.
Shell equivalve, closing tightly, with umbones often eroded,
covered with a periostracum, not pearly, trigonal or roundly
ovate ; hinge usually bearing two or three cardinal teeth and both
anterior and posterior laterals ; ligament external, prominent;
pallial line simple or sinuous.
Animal fluviatile, lacustrine or estuarine; with anteriorly open
mantle; generally furnished with t«o siphons of variable size,
seldom a single (anal) one; foot large, without byssus in the adult
state; palpes triangular; gills joined behind, unequal, the outer
the shorter.
Distribution. Asia ; Africa ; America ; Australia.
Genus CYRENA.
Cyrena, Lamarck, Anim. s. Vert, v, 1818, p. 551.
Venus (pars), Chemnitz, Martini & Chemnitz, vi, 1782, p. 333,
pi. 32, fig. 336.
Cyclas (pars), Bruguiere, Encycl. Metli. 1792.
Cyanocyclas, Ferussitc, Diet. Sci. Nat. xii, 1818.
Polymesoda, Kafinesqiie, Ann. (len. Sci. Phvs. et Nat. v, 1820,
p. 219.