| 1. | A description is given of Gyrocotyle rugosa Diesing, 1850, a cestodarian parasite of the elephant fish. Callorhynchus milii (= C. antarcticus). It is morphologically clearly distinct from the other species in the genus. |
| 2. | The lycophore larva of G. rugosa is described. It has three pairs of transparent vesicles, considered to be gland cells, in the anterior half of the body; a large bilobed organ; relatively large hooks; and one pair of flame cells. |
| 3. | Numerous postlarval stages, 0.225 to 0.957 mm. in length, were found in the scrapings of mucus from the anterior part of the spiral valve of the host. In 16 hosts examined, no specimens were found between this size and adult specimens. |
| 4. | Eggs of G. rugosa hatch almost immediately in sea water. The ciliated lycophore larvae showed no interest in one species of bivalve, one species of hermit crab, and one species of snail. They penetrated and remained in very large numbers in scrapings of mucus from the spiral valve of the elephant fish. |
| 5. | Lycophore larvae readily penetrate into the tissues of pieces cut from the spiral valve of the elephant fish. With few exceptions, they enter into the muscular layers rather than into the mucosal layers. Within an hour, at least four larvae had entered blood vessels, and these had travelled some distance from their point of entry. |
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