In some cases it is difficult to recognise a species because no type material is known to compare collected specimens against. Sometimes one has to be lucky, e.g. by finding material in old collections that can be traced back as (probable) types.
Borrero & Araujo (2012) describe at length such a case where in total three specimens have been found in two different museums, of what they consider to be Isomeria morula (Hidalgo, 1870). A lectotype has now beem selected from the material in the Madrid museum to define the taxon, and the taxonomic position is clarified.
The text of the abstract reads: A clarification of the status of Isomeria morula (Hidalgo 1870) is given, based on the recently rediscovered, likely type specimen at Museo Nacional de Ciencias Naturales (MNCN, Madrid, Spain), and additional material from University of Michigan Museum of Zoology (UMMZ, Ann Arbor USA). The available material (three specimens) comes from older collections (i.e., mid- to late 1800???s) from Ecuador. The specimen at MNCN is here designated as the lectotype of I. morula (Hidalgo 1870). Conchological characteristics are discussed and this species is fully illustrated for the first time. Comparisons of this taxon with other Isomeria from western South America and a partial key are also given, thus contributing to clarifying its status and recognizing it from other species in the genus. The geographic distribution of I. morula and its conservation status remain unknown.
Borrero, F.J. & Araujo, R., 2012. Clarification of the taxonomic status of Isomeria morula (Hidalgo, 1870), from Ecuador (Gastropoda, Pleurodontidae). – Journal of Conchology 41: 145-152.