Two new species of Thaumastus (Thaumastus) from the state of Minas Gerais, southeastern Brazil, are described. They are diagnosed and characterized by the morphology of the shell and soft parts and compared with Brazilian species of the subgenus Thaumastus s.s. Martens, 1860. Thaumastus (T.) parvus sp. nov. is similar to T. (T.) baixoguanduensis Pena, Coelho & Salgado, 1996 but can be distinguished by the smaller size, smaller number of plates in the jaw, different number of follicle groups in the ovotestis and form of the fertilization complex. Thaumastus (T.) caetensis sp. nov. is similar to T. (T.) largillierti (Philippi, 1845) but differs by the width and the contour of the parietal side of the shell aperture. T. (T.) caetensis is also closer to Thaumastus (T.) baixoguanduensis but can be distinguished by the smaller dimensions (height, width and number of protoconch whorls), the lack of a transversal light band on the body whorl, the jaw with smaller number of plates, and the radula with 35 teeth. In the soft parts, this new species differs also in the number of follicle gatherings in ovotestis, fertilization complex with globose shape, and penian retractor muscle terminally and laterally attached to flagellum

Uma nova espécie de Thaumastus (Thaumastus) Martens, 1860, do Estado de Minas Gerais, Brazil, é descrita e ilustrada, com base na morfologia da concha, mandíbula, rádula e partes moles.

A new species of Thaumastus (Thaumastus) Martens, 1860, from Minas Gerais State, Brazil, is described and illustrated, based on the morphology of the shell, jaw, radula and soft parts.

Strophocheilus miersi Da Costa, 1904 é recaracterizado pela conquiologia e pela primeira vez a morfologia das partes moles. Complexo palial, sistemas reprodutor e digestivo forneceram importantes caracteres para enriquecer o conhecimento sobre Strophocheilus Spix, 1827. A presençca de quatro pregas arqueadas na região posterior da massa cefalopediosa e a morfologia da glândula suprapediosa acrescentaram dados para a diagnose da espécie.

Stropocheilus miersi Da Costa, 1904 is recharacterized by the conchology and morphology of the soft parts, the latter for the first time. Palial complex, reproductive and digestive systems provide important characteristics to enrich the knowledge of the genus Strophocheilus Spix, 1827. The presence of four arched folds in the posterior region of the pediose mass and the morphology of the suprapediose gland offered more data to identify and diagnose the species.

Synapterpes (S.) hanleyi (Pfeiffer, 1846) is characterized by anatomy, synonymy and geographical distribution. Shell and soft parts were studied and important taxonomic characters evaluated and illustrated. These studies give conditions to characterize the species and include it in the genus Synapterpes Pilsbry, 1896 and distinguish S. hanleyi from the other species of Synapterpes s.s. known only by their shells, respectively from Brazil and Colombia: S.(S.) coronatus (Pfeiffer, 1846) and S.(S.) wallisi (Mousson, 1869).

Studies on specimens from Brazil (States of Pernambuco and Alagoas) were carried out in order to relate data about morphology of hard and soft parts o Nocyclotus (N.) agassizi (Bartsh & Morrison, 1942).