mycetopodiDjE. 243 



SPATHA, Lea, 1838. Shell oval, thick; cardinal mai-gin arcuated 

 and nearly smooth. Outer gill united to the mantle as far as 

 its extremity ; inner gill not united to the foot. S. ruhens, Lea 

 (cxxiv, 8). E. Africa. 



LEILA, Gray, 1842. (Columba, Lea.) Shell oval, inflated, very 

 inequilateral, gaping, with prominent beaks ; cardinal margin 

 straight, simple. L. Blainvilleana, Lea (cxxiv, 5). So. 

 America. 



? HAPLOTHfERUS, Conrad, 1814. Equivalve ; hinge-margin 

 straight, cartilage-area very broad and thick, hinge edentulous ; 

 anterior muscular scar small, narrow, and deeply impressed, 

 accessory situated under the primarj^ scar. H. capax, Conr. 

 (cxxv, 8, 9). Fossil; Pebas Group, Upper Amazon. Described 

 from fragments ; the portion containing the posterior muscular 

 impression is missing. 



Triquetra, Klein, lt53. 



Syn. — Syria, Lam., 1819. Pachyodon, Schumacher, 181*7. 

 Triplodon, Spix, 1827. 



Distr. — 4 sp. South America. T. amcuZarzs, Lam. (cxxiv, 2). 

 T. cor^rugata, Lam. (cxxiv, 1). 



Shell Area-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. 



Prisodon, Schum.,18n. 



Syn. — Tetraplodon, Spix, 1827. Castalia, Lamarck, 1819. 



Distr. — 3 sp. Rivers of South America, Guiana, Brazil. F. 

 ambigua, Lam. (cxxiv, 3, 4). 



Shell ventricose, trigonal; umbones prominent, furrowed; 

 hinge-teeth striated ; anterior 2*1, short ; posterior 1-2, elongated. 



Animal with mantle-lobes united behind, forming two distinct 

 siphonal orifices, the branchial cirrated ; outer gill united to the 

 mantle as far as its extremity ; buccal appendages rounded, very 

 large ; foot much compressed, thicker and bent behind. 



Arconaia, Conrad, 1865. 



Di^tr. — A. (Triquetra) contorta, Lea (cxxv, 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). 



Family MYCETOPODIDJE. 



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. 



