species vvith absolute certainty, to separate it from a closely allied form taken in the same or 

 in another sea. Therefore I give a detailed representation of the petasma in every species. As 

 the organ is very complicate in the genus Sergestes, white it is more or less reduced in the other 

 genera, it will be expediënt to give a description of the petasma in the general treatment of the 

 genus named, and later on at each of the other genera to mention its reduction or structure. 



I. Sub-Family Sergestin^;. 

 Sergestes H. Milne-Edw. 



This genus was established in 1830 by H. Milne-Edwards (Ann. Sci. Natur. t. XIX, 

 1830) on a single species. Since that remote year numerous authors have published larger or 

 smaller contributions to our knowledge, but among them only some of the most important are 

 mentioned here. — In 1859 a valuable paper was published by Henrik Kröyer (Forsog til en 

 monographisk Fremstilling af Kraebsdyrslaegten Sergestes, in: K. D. Vidensk. Selsk. Skrifter, 5. 

 Reekke, naturv.-math. Afd., 4. B.), in which he described and figured on five plates 15 species, 

 all new, but the majority of them briefly characterized by him in a preliminary paper in 1855. — 

 In three papers published 1882 — 86 S. J. Smith gave excellent descriptions with good figures 

 of 3 species from the Atlantic. — In 1888 the great work by C. Spence Bate on Decapoda 

 Macrura (Rep. Voy. "Challenger", Zool., vol. XXIV) wasissued, in which a very large con- 

 tribution to our knowledge of Sergestes and its larval forms is found; the author established 

 in all 24 species of Sergestes as new. — Some years after I wrote a treatise on this genus 

 (On the Development and the Species of the Crustaceans of the genus Sergestes, in : Proc. 

 Zool. Soc. London, Dec. 1, 1896). It contains a review of the whole literature from 1830 to 

 1895 and an enumeration of all species, in all 59 (or, if the dead-born genus Sciacaris Bate is 

 included, 60 species) of the genus Sergestes. Furthermore it is proved that only about 20 of 

 these species have been established on adult animals, and that some of these species must be 

 cancelled as synonyms, while the remaining majority, nearly two scores of species, had been 

 founded on larval forms in the MastzgoJ>tts-sta.ges ; besides it was shown that some of the larvae 

 established as separate species are Mastigo/>its-stages of species already known as adults, while 

 other larvae belong to forms unknown in the adult stage. Finally, based on the literature and 

 on a rich material of adults and larvae of forms living- near the surface and belonging- to the 

 • Copenhagen Museum, I gave a view of all forms. — A later publication of mine (H. J. Hansen: 

 The Crustaceans of the genera Petalidiiim and Sergestes from the 'Challenger', with an account 

 of luminous organs in Sergestes challengeri n. sp., in: Proc. Zool. Soc. London, Jan. 20, 1903) 

 contains a critical revision of the "Challenger" material preserved in the British Museum (Natural 

 History); its most important point is the discovery of a large number of complex luminous 

 organs in a single form. — It is deemed unnecessary to enumerate here the numerous papers 

 published since 1895, which contain contributions on Sergestes \ some among them are quoted 

 on the following pages. 



