Dictionary of Ichthyology  

egg-case = the keratinous egg shell of Myxini, Elasmobranchii and Holocephali containing the developing embryo. 

Egg case of Port Jackson shark, Heterodontus philippi (= H. portusjacksoni) from "A Guide to the Study of Fishes" by D. S. Jordan, 1905. Photograph by Brian W. Coad.

Canadian Museum of Nature www.briancoad.com