BV \V. A. IIASWKLL. 341 



— and that quite a near one — lives on European lobsters (Nephrops and Homarus) . 

 But structurally the marine Hydrachnid genera — Pontaraclma and Nautara-chna — 

 seem kss remote than the rest of the marine Acarids — the Halacaridae. 



Such eases of parasitism as are known in the Hydrachnids have little analogy 

 with the case of Astacocroton. Many of them are cases in which the parasitism 

 is confined to the larval stage. In the ease of various species of Atax and of 

 Naiadicola ingetis, in which the young become parasitic on the gills of fresh- 

 water mussels, the parasitism may be continued to the adult condition. But there 

 is nothing to connect any of these structurally with Astacocroton; if that genus is 

 to be set down as a parasitic Hydrachnid, it seems to have no close relationship 

 with any Hydrachnid hitherto known. 



Literature * 



Banks, N., 1904. — Treatise on Aearina or Mites. Proc. U.S. National Museum, 



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 Beneden, p. J. van, 1850. — Recherohes sur I'histoire naturelle et le developpement 



de VAtax ypsilophora. Mem. Acad. Roy. Belg., t. 24. 

 *Berlese, Ant., 1896. — Ricerche sugli organi e sulla funzione della digestione 



negli Acari. Portici. 

 Bernard, H. M., 1894. — Some observations on the relations of the Aearidae to 



the Araehnida. Journ. Linn. Soc, ZooL, vol. 24. 

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Journ. Boy. Microsc. Soc. 

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Soc. Zool. Framce, t. 14. 

 Haller, G., 1881. — Die Mundtheile und Systematische Stellung der Milben. Zool. 



A71Z., 4 Bd. 

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Zeitschr. f. viiss. Zool, 70 Bd. 

 Henking, H.. 1882. — Beitriige zur Anatomie, Entwickelungsgesehichte und Bio- 



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Zool., 37 Bd. 

 KOENICKE, F., 1881. — Steissdriisen von Atax crassipes. Zool. Anz., 4 Bd. 

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Zool. Anz., 15 Bd. 

 Kramer, P., 1875. — Beitrage zur Naturgesehichte der Hydrachniden. Archiv. f. 



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Bd. 

 Michael, A. D., 1895. — A study of the internal anatomy of Thyas petrophilus, 



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Zool., vol. 6. 

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'Titles marked with an asterisk are papers of which the contents are known 

 to me only from abstracts in the Zoologischer Jahresbericht. 



