1. Beard J (1890) On the development of the common skate Raia batis. In: 8th annual report, Fisheries, Scotland
2. Bessels E (1869) Ueber fossile Selachier Eier. Ver vaterl Naturkunde Wurttemberg Jahresh 25:152–155
3. Böttcher R (2010) Description of the shark egg capsule Palaeoxyris friessi n. sp. From the Ladinian (Middle Triassic) of SW Germany and discussion of all known egg capsules from the Triassic of the Germanic Basin. Palaeodiversity 3:123–139
4. Brown RW (1946) Fossil egg capsules of chimaeroid fishes [From Germany, Wyoming, New Mexico, Montana, and Alaska]. J Paleontol 20(3):261–266
5. Brown CH (1955) Egg capsule proteins of selacians and trout. Quart J Microsc Sci 96:483–488