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different structure of the last pair of nropoda, and that nf the telsmi. The 

 species of tliis genus are still more difficult to distinguish from each other, 

 exliibiting, as they do, a very uniform appearance, and agreeing almost exactly 

 in tlie structure of the last pair of pereiopoda, which, in Ampelisca, affords 

 one of the most easily reeognizalile distinguisliing marks. The mutual lon- 

 gitudinal relation of the antennte, the form of the last pair of epimeral plates of 

 metasome, and the structxtre of the last pair of uropoda, and that of the telson, 

 are, chiefly, those characteristics by which the species may be more clearly 

 distinguished from each other. Besides the typical form, B. Gaimnrdii of 

 Kroyer, a few species have been characterized in the latter time by diifereut 

 auth(U's. Thus a species, nearly related to B. Gaimardii, has been recorded 

 from the American coast, as B. serrata Smith; another form was described by 

 Metzger from the North Sea as B. crasmcornis, and a third species has recently 

 Ijeen cliaracterised by Chevreux, from the Expedition of Hirondelle, as B. 

 Gurrni. I have myself examined no less than 7 species occurring off the 

 Norwegian coast, to be described in the sequel. 



U. Byblis Gaimardii, (Kroyer). 



(PI. C4). 

 Ampelisca Gaimardii, Kroyer, (T.airaavd's Voyages en Soandiuavie, PI. 23, fig. 1. 



Form of body very slender, especially in the male. Cephalon much 

 shorter than the 3 anterior segments of mesosome combined, front transversely 

 truncated, with the lower corner blunted. Anterior pairs of coxal plates very 

 little deeper than the correspomling segments, 1st pair obliquely expanded 

 di.stally, and advancing along the sides of the cephalon, terminal edge strongly 

 arched in front and densely fringed with long and slender bristles; 4th pair 

 considerably more broad than deep, terminal edge but slightly curved. Last 

 pair of epimeral plates of metasome broadly truncated at the lateral corners. 

 First segment of iirosome somewhat gibbous at the end dorsally. Corneal 

 lenses very large and refracting, the lower jiair occupying the inferior corners 

 of the front; underlj'ing pigment lu'ownish, witli a darker ring encircling the 

 lenses. Superior antenna^ in female aliout eijualling in length the third part 

 of the bod}', and scarcely more than half as long as the inferior, 1st joint of 

 the i)eduncle short and thick, 2nd about twice as long, and much more slender, 

 last one small, and reaching a little beyond the middle of the penultimate 

 peduncular joint of the infei'ior ones, flagellum twice the length of the peduncle, 

 and composed of about 20 articulations. Inferior antennsE in female about 

 eciualling in length ^/i of the body, last joint of the peduncle sh<n-ter than 

 the penultimate one. Antennae in male much more elongated, the inferior ones 



