118 DR. H. J. HANSEN ON THE INaOLFIELLID^, 



Dr. Th. Mortensen on tlie shore of one of the islands in the Grulf 

 of Siam. In the report on the Crustacea collected by the ' Ingolf ' 

 to be published in the future, I could scarcely include the Siamese 

 species, and I resolved therefore to give a separate account of 

 both forms. The type deviates so much from other Amphipoda in 

 several particulars, that the publication of this treatise on the 

 family may be justified. 



It may be convenient to begin with the description of the two 

 species ; secondly, to point out the essential characters of the 

 type, comparing it with other Amphipoda ; then to supply a 

 diagnosis of the new family ; finally to set forth some remarks on 

 the tribes of the Amphipoda and the place and rank of the 

 Ingoljiellidcs, fam. nova. 



I. Description of tlie Species. 



1. iNGOLriELLA ABTSSi, u. gen. et n. sp. (PL 14. figs. 1-18 ; 

 PI. 15. figs. 19-21.) 



Body (fig. 1). — The animal is very elongate, between fourteen 

 and fifteen times longer than deep, round, thus being filiform, and 

 without processes or tubercles ; hairs are not to be found on the 

 head, the thorax or the abdomen, the telson excepted. The first 

 thoracic segment is considerably deeper in front than posteriorly, 

 more closely connected with the head than with the second 

 thoracic segjtnent, yet sharply separated from the head, but the 

 movement which may be possible between these two parts must 

 at most be rather feeble. The second thoracic segment is much 

 longer but not deeper than the first, one and a half times longer 

 than deep ; from this segment to the third segment of the 

 abdomen the segments increase gradually somewhat in depth, 

 and the last-named segment is as long as the sum of the second 

 thoracic segment and one half of the first segment, but not quite 

 twice as deep as the second. The third abdominal segment has 

 the lower portion of the postero-lateral margin very oblique, 

 without vestige of any angle, and the following segments decrease 

 posteriorly in depth and length. The abdomen is slightly 

 shorter than the combined length of the six posterior thoracic 

 segments ; its segments are all excellently defined. The thoracic 

 ' epimera ' are not developed as plates, but only as small basal 

 joints of the legs. 



Head (fig. 2). — It is more than one and a half times longer 

 than deep; rounded. A small angle is developed dorsally between 



