The Class Pentastomida is ranked under the Phylum Arthropoda by most authors, but its position is questionable in view of its unusual body structure, and probably the group should be regarded as occupying an isolated place among the invertebrates. The members of the Class Pentastomida are endoparasitic in the respiratory passages and lungs of vertebrates. They are veriform with flattened cylindrical annulated body; they are unique in that the body is non-segmented, but the muscles are metamerically arranged and the integument is chitinous with numerous glands. These data alone would justify the argument that they should be assigned an isolated place among the invertebrates. Pentastomid parasites in Indian lizards are meagerly known today. Very few reports have been made on the occurrence of Raillietiella in India lizards. In view of the need for a better understanding of the taxonomy, anatomy, and biology of a common Indian pentastomid parasite the present investigation was undertaken; this paper constitutes the third in a series entitled “Parasites of Reptiles.” The studies, however, are not complete, and only the taxonomy and anatomy of the parasite are discussed in detail. The form in question is easily obtainable in the environs of the city of Madras, India, where the incidence of the infection on the lizard, Calotes versicolor, appears to be high. Besides, the parasite would form a highly suitable material for the study of pentastomids in the laboratory. In as much as the pentastomid, Raillietiella, is not known to occur in Calotes versicolor, the present paper records for the first time a new host for the genus Raillietiella. The investigator has taken an independent stand from Anantaraman (Anantaraman and Krishnaswami 1958) in naming the present pentastomid parasite as a new species.