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XLIIL— NOTE ON THE AKEANGEMENT OF THE MESEN- 

 TEEIES IN THE PAKASITIO LABVA OF HAL- 

 CAMP A CHRYSANTHELLUM (Peach). By A. C. 

 HADDON, M.A., M.E.I.A., Professor of Zoology in the 

 Boyal College of Science, Dublin. (Plate XL) 



[Read, February 16, 1887.] 



In 1859 L. Agassiz recorded from the east coast of North America 

 an Actinia parasitic on Medusae, which he named Bicidium para- 

 sitica. This has since been found by Verrill in 1862, and by 

 A. Agassiz in 1865. Still more recently (1884), Mark 1 has given 

 a preliminary account of a larval Edwardsia, which is parasitic 

 within the gastro-vascular canals of the Ctenophore Mnemiopsis 

 leidyi. 



On this side of the Atlantic, T. Strethill Wright, in 1859, gave 

 an account of a small Actinia, also parasitic, on Hydromedusse,- 

 from the Firth of Forth, which he named Halcampa Fultoni; and, 

 in the following year, F. Muller described a similar form, which 

 he named Philomedusa vogtii, from the Santa Catherina, on the 

 Italian Riviera. E. Graeffe described, in 1883, a parasitic Hal- 

 campa from the Adriatic, which, " as the development of Halcampa 

 chrysant helium is not known, this form must, provisionally, be 

 separated from H. chrysanthellum as H. mediisophila." 



The author exhibited, and made remarks upon, two specimens 

 of a parasitic Halcampa at a meeting of the Royal Irish Academy, 

 on June 22, 1885, and a record was published in the following 

 year. In this communication it is stated that Prof. A. Macalister 

 of Cambridge (late of Dublin) had informed the author, by letter, 

 that he had met with this Halcampa, and perhaps another form, 

 but neither of them in Dublin Bay. Specimens were also obtained 

 in Dublin Bay in June, 1886, and on June 6, in the same year, off 



1 " Selections from Embryological Monographs," compiled by A. Agassiz, W. 

 Faxon, and E. L. Mark, Bull. Mus. Comp. Zool., Harvard Coll. (Camb., U. S. A.), 

 p. 43, pi. xii. 



