The prairie rattlesnake, Crotalus viridis, was found to be commonly infected with third-stage Physaloptera larvae. A total of 112 larvae were fed to 3 laboratory raised cats. Adult worms recovered 42 and 59 days postinfection were identified as P. rara. Observations were made on the pathology of the larvae in the snake.

The fine structure of the M and C forms of seal poxvirus as observed in negative stained preparations in the electron microscope are described. The M form has a beaded surface and a serrated outline and particles averaged 312.3 mμ in length and 193.8μ in width. The C form was not beaded, had a serrated periphery and averaged 352.8 mμ in length and 196 mμ in width. A short discussion of the morphology of seal poxvirus in relation to other poxviruses is presented.