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majority are small, with one or very few genera and i-ather few species, but the family 

 Phoxocephalidse is pretty considerable, the tiunily Podoceridae is lai'ge, and the family 

 Lysianassidse is exceedingly large (in Sars' work lliirty-three genera), wherefore it seems 

 interesting to me that no parasite of our Choniostomatidse has been found on any species 

 belonging to these families. One species was found in the Mediterranean in the genus 

 Microdaiitop'us Costa, belonging to the Photidse, another species has been quite recently 

 discovered in Cyclaspis G. 0. S., belonging to the family Cumidsp, and these genera are the 

 only two mentioned in the literature of the subject, in which I have not i)ersonally observed 

 the parasites of tliis family. To give an account of the foinis the examination of which led 

 to no result, would be too tedious, neither would it prove much; I will only say that I have 

 examined a good number of exotic species, most of which were only represented by a few 

 specimens, besides nearly all of the large material our museum possesses of Gammaridea 

 from Denmark, Greenland and the Kara Sea, and many of these species were represented 

 by from fifty to hundieds of specimens. In F. Meineit's thi'ee papers, of 1877, 1880 

 and 18iJ0 respectively, about Danish Malacostiaca, and in my own similar papers about the 

 fauna of Western Greenland and of the Kara Sea, will be found the names of most of the 

 northern and arctic species examined, of which I have had a large matei-ial. 



In a later paragi-aph I shall mention a little more in detail the following pheno- 

 menon which stands in a certain connection with the matter above, namely, that of several 

 species a considerable material from a large sea can l)e examined without showng a single 

 parasite, whereas sometimes a smaller material of the same species from another sea reveals 

 sevei'al parasites. This proves that we cannot conclude that a species is not infested, fi'om 

 the fact that an investigation of hundreds of specimens Irom ditierent localities of a certain 

 country has not led to the discovery of any parasite. In most cases such examinations must 

 be undertaken on a much lai'ger scale than I \m\& been able to do, before any value can 

 be attached to the negative results. 



b. Age and Sex of the Hosts. 



It serves our purpose best to divide the hosts into two sections according to their 

 parasites, viz. whether the typical residence of these animals is in the marsupium or in other 

 places. I will begin by the latter section, repeating my above statement tliat I only have 

 examined five species of parasites which do not live in the marsupium. 



Aspidoecia Normani, ^^liich, as has just been said, lives on the outside of the body 

 of species belonging to the genus Erylhropf', I have found on young specimens as well as 

 on adult males and females, but in the latter the marsupium was eitlier empty, oi' occupied 

 by a species of the genus Mysidion. The two species of the genus Choniosiomu li\e in the 

 branchial cavity of two species of the genus Hij)j)oJytc. From the Kara Sea I have seen 



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