434 MANUAL OF THE MOLLUSCA. 
were usually found in old and deformed specimens; round 
nearls about the size of a pea, perfect in every respect, were 
worth £3 or £4. (Dr. Knapp.) Anaccount cf the Irish pearl- 
‘ishery was given by Sir R. Redding, in the Phil. Trans., 1693. 
The mussels were found set up in the sand of the river-beds with 
their open side turned from the torrent ; about one ina hundred 
might contain a pearl, and one pearl in a hundred might be 
tolerably clear. (See p. 30). 
Distribution, 420 species. North America, South America, 
Europe, Africa, Asia, Australia. 
Fossil, 50 species. Wealden —. Europe, India. 
Sub-genera, Monocondylea, D’Orbigny. M. Paraguayana, 
Hele xey ir, Fis. 2. 
Shell with a single large, round, obtuse cardinal tooth in each 
valve; no lateral teeth. 
Distribution, 6 species. South America. 
Hyria, Lam. H. syrmatophora, Pl. XVIII., Fig. 3. Synonyms, 
Pachyodon and Prisodon, Schum. Sheil Arca-shaped, hinge-line 
straight, with a dorsal wing on the posterior side; teeth elon- 
gated, transversely striated. Distribution, 4 species. §. America. 
CASTALIA, Lamarck. 
Type, C. ambigua, Pl. XVITI., Fig. 4. 
Synonym, Tetraplodon, Spix. 
Shell ventricose; trigonal; umbones prominent, furrowed ; 
hinge-teeth striated; anterior 2.1, short; posterior 1.2, elon- 
gated. 
Animal with mantle-lobes united behind, forming two distinct 
siphonal orifices, the branchial cirrated. 
Distribution, 3 species. Rivers of South America, Guiana, 
Brazil. 
ANODON, Cuvier. Swan-mussel. 
Type, A. cygneus, Fig.:208, p. 398. 
Etymology, anodontos, edentulous. 
Shell like wnio, but edentulous; oval, smooth, rather thin, 
compressed when young, becoming ventricose with age. 
Animal like unio: the outer gills of a female have been com- 
puted to contain 300,000 young shells. (Lea.) Seep. 14. 
Distribution, 100 species. North America, Europe, Siberia. 
Fossil, 8 species. Hocene—. Europe. 
M. D’Orbigny relates that he found great quantities of small 
Anodons (Bysso-anodonta Paraniensis, D’Orbigny) 4 lines in 
length, attached by a byssus, in the River Parana, above 
Corrientes. 
