THE SERGESTID£ OF THE SIBOGA EXPEDITION 



BY 



H. J. HANSEN, 



Gjentofte (near Copenhagen). 



With 5 plates and 14 text figures. 



This well defined and most interesting family has with good reason been divided into 

 two sub-families: Sergestinae and Luciferinse. The first sub-family comprises four genera: 

 Sergestes H. Milne-Edw., Petalidium Sp. Bate, Sicyonella Borradaile (Apkareocaris Calm.) and 

 Acetes H. Milne-Edw., while the genus Liicifer Vaughan Thomson {Leucifer H. M.-Edw.) 

 constitutes the Luciferinse. With exception of Petalidium all genera are represented in the 

 "Siboga" collection. Ot Sergestes, Sicyonella and Acetes the expedition has secured a good 

 material, containing some undescribed species, while the collection of Ltuifer is exceedingly rich. 

 The Zoological Museum in Copenhagen possesses of the genera in question a good material, 

 which in many cases has been most useful for comparison, and with the kind allowance of the 

 Editor of the "Siboga" work I have even been able to include in the present paper descriptions 

 with figures of forms — most of them from the Indo-Chinese seas — not gathered by the 

 "Siboga"' of the hitherto imperfectly known genus Acetes. As the degree of our knowledge of 

 the four genera is very different, it is found adequate to deal with each genus according to 

 the state of the literature. 



In the treatment of the genera and species I have introduced a special study ot the male 

 copulatory organs on the first pair of pleopods, the petasma. Various authors have published 

 a more or less good outline of the petasma of a single form or of two species, but only one 

 author, S. J. Smith, has given a more detailed representation of the petasma in a single species 

 [Sergestes roèusttcs Smith), and nobody has attempted a comparative investigation in any of 

 the genera. As in the order Euphausiacea, the petasma has shown itself to afford as a rule 

 the best and most reliable specific characters; it is always very important, and in some cases 

 it is even absolutely necessary to possess an adult male in order to be able to determine a 



SIBOGA-EXPED1T1E XXXVIII. 



.'4832 



