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Genus Quadrulella

Shell is pyriform, or elongated pyriform, with the lateral sides tapering towards the aperture, with or without distinct neck. Always laterally compressed, elliptical in cross section. Aperture ranging from linear to strongly curved, with or without thickened organic lip. Shell is hyaline, composed of self-secreted square plates. Quadrulella differs from Nebela and Hyalosphenia by the use of square, siliceous self-secreted plates in the construction of the shell. It may be confused with Mrabella, which has similar shell shape and square plates. The most distinctive characteristic is the presence of a lateral pronounced hollow keel in the genus Mrabella (although Q. alata also exhibits a lateral keel, we consider it to be flat and not hollow, even if this detail is not mentioned in the original description of the species), and the fact that square plates of Quadrulella are self-secreted, while the origin of square plates of Mrabella is unclear. Type species: Quadrulella symmetrica (Wallich, 1864) Cockerell, 1909