52 DR. H. J. HANSEN ON CRUSTACEANS [Jan. 20, 
7. On the Crustaceans of the Genera Petalidium and Sergestes 
from the ‘Challenger,’ with an Account of Luminous 
Organs in Sergestes challengeri, n. sp. By Dr. H. J. 
Hansen (Copenhagen). 
[Received November 29, 1902. ] 
(Plates XI. & XII.") 
During a stayin London in July and August, 1902, I examined 
various groups of Crustacea in the British Museum (Natural 
History). I beg the Director, Professor E. Ray lLankester, 
and Mr. F. Jeffrey Bell to accept my sincere thanks for the free 
use of the collection and for their kind help. 
In the paper “On the Development and the Species of the 
Crustaceans of the Genus Sergestes” (Proc. Zool. Soc. Lond. 
1896, pp. 936-70) I have given a revision of this extensive 
genus. I had studied a very rich material of pelagic forms 
belonging to the Copenhagen Museum, among which are all the 
types of Kroyer; besides I had examined types of 5 species 
established by Chun, Metzger, and Ortmann. 
Among other things, I proved that ‘of the 59 (or 60) hitherto 
described species only about 20, or one-third of the total number, 
have been established on adult animals, such as have almost or 
entirely arrived at sexual maturity ; and that almost all the other 
species are true larve, and even of these a considerable number are 
larval stages of species already established on adult specimens, .. .” 
Of earlier authors, C. Spence Bate has produced a very large con- 
tribution on the genus Sergestes, extending to eighty-eight quarto 
pages and seventeen plates, in his ‘“ Report on the ‘Challenger’ 
Macrura.” He established the genus Petalidiwm on a new species, 
described 24 new species of Sergestes &c. In 1896 I wrote 
(p. 939): ‘This large contribution is of course of great 
importance, but unfortunately neither the descriptions nor the 
figures are so good as could be wished, and in numerous instances 
...a re-examination of the type specimens is absolutely necessary 
—the greater part of the new species are but larve.” I have now 
studied all types which are preserved in the British Museum, and 
the present paper contains the results of my examination. 
Bate describes 31 species of Sergestes as examined by himself : 
of these, 24 are established as new to science, 6 are considered 
to be Kroéyerian species, and one is referred to S. atlanticus 
H.M.-Edw. The types of 9 of the species established by Bate do 
not exist in the British Museum; some specimens mentioned in 
his work and belonging to other species are also absent; but 
several specimens belonging to various species and omitted in the 
Report were found in the collection. I am therefore only able 
to give more or less incomplete notes, based on the study of the 
1 For explanation of the Plates, see p. 78. 
