440 
CONCHIFERA. 
with blue or purple; internal margin blue, the concave part 
white. Two to three inches long. Inhabits the British seas. 
Genus 29.—MODI OLA.— Lamarck. 
Generic Character. —Subtrarisverse, ecpiivalve, regular; the 
posterior side very short; beaks nearly lateral; hinge without 
teeth, lateral and linear; ligament placed in a marginal furrow, 
and nearly interior, with one muscular impression in each valve 
which is sublateral and elongated. 
Modiola cliscors. — The Discordant Modiola. 
Plate LXXXVIII. fig. 17. 
Oblong-oval, very convex, produced and narrower at the an¬ 
terior end ; longitudinally striated on both sides, and transverse¬ 
ly in the middle ; outside green ; inside white or pale pink, and 
somewhat pearly ; margin crenulated at the base ; the beak ob¬ 
lique. One half inch long. Inhabits the British seas. 
TRIBE III.-TRIDACNITES. 
Transverse, equivalve, the muscular impressions situated 
under the centre of the lower margins, and extended on each 
side. 
Genus 30. — HIPPOPUS. — Lamarck. 
Generic Character .—Equivalve, regular, inequilateral and 
transverse; lunule closed; hinge with two compressed unequal 
teeth ; ligament marginal, and external. 
Hippopus maculalus. — The Spotted Hippofus. 
Plate LXXXVIII. fig. 18. 
Transversely ovate, ventricose, with scaly ribs; and reddish 
purple spots ; lunule cordated, heart shaped, and oblique ; the 
margins very deeply crenulated. Eight inches broad. Inhabits 
the Indian seas. 
Genus 31.—TRIDACNA.— Lamarck. 
Generic Character. —Shell regular, equivalve, inequilateral 
and transverse ; a gaping space near the beaks ; hinge with two 
compressed, unequal teeth ; ligament marginal and external. 
