MYCETOPODIDA. 243 
SPATHA, Lea, 1838. Shell oval, thick; cardinal margin arcuated 
and nearly smooth. Outer gill united to the mantle as far as 
its extremity ; inner gill not united to the foot. S. rubens, Lea 
(exxiv, 8). E. Africa. 
LEILA, Gray, 1842. (Columba, Lea.) Shell oval, inflated, very 
inequilateral, gaping, with prominent beaks; cardinal margin 
straight, simple. JL. Blainvilleana, Lea (exxiv, 5). So. 
America. 
? HAPLOTH@RUS, Conrad, 1874. Equivalve; hinge-margin 
straight, cartilage-area very broad and thick, hinge edentulous ; 
anterior muscular scar small, narrow, and deeply impressed, 
accessory situated under the primary scar. H. capax, Conr. 
(exxv, 8,9). Fossil; Pebas Group, Upper Amazon. Described 
from fragments ; the portion containing the posterior muscular 
impression is missing. 
TRIQUETRA, Klein, 1753. 
Syn.—Hyria, Lam., 1819. Pachyodon, Schumacher, 1817, 
Triplodon, Spix, 1827. 
Distr.—4 sp. South America. T. avicularis, Lam. (cxxiv, 2). 
T. corrugata, Lam. (exxiv, 1). 
Shell Arca-shaped, hinge-line straight, with a dorsal wing on 
the posterior side; hinge with cardinal and lateral teeth, the 
latter serrated. Mantle-lobes united together behind and. fur- 
nished with two short, contractile siphons. 
Prisopon, Schum., 1817. 
Syn.—Tetraplodon, Spix, 1827. Ohatatta: Lamarck, 1819. 
Distr. —3 sp. Rivers of South America, Guiana, Brazil. P. 
ambigua, Lam. (cxxiv, 3, 4). 
Shell ventricose, trigonal; umbones ponent, furrowed ; 
hinge-teeth striated ; anterior 2°1, short ; posterior 1-2, elong ated. 
Animal with mantle-lobes united behind, forming two distinct 
siphonal orifices, the branchial cirrated ; outer oill united to the 
mantle as far as its extremity ; buccal appendages rounded, very 
large ; foot much compressed, thicker and bent behind. 
ArconatA, Conrad, 1865. 
Distr.—A. (Triquetra) contoria, Lea (exxv, 16,17). China. 
Shell elongated, bent or bow-shaped ; hinge with two distant, 
oblique, robust, short cardinal teeth, finely rugose-striate ; lateral 
teeth elongated, minutely rugose- striate (not serrated). 
Famity MYCETOPODID A. 
Shell thin, soleniform, transversely elongated, gaping at both 
extremities ; hinge-line straight, linear, without teeth. 
Animal with greatly developed foot, ending in a disk-like 
expansion. 
