936 DR. H. J HANSEN ON CRUSTACEANS [Dec. 1, 
6. On the Development and the Species of the Crustaceans 
of the Genus Sergestes. By Dr. H. J. Hansen (Copen- 
hagen)’. 
[Received October 15, 1896.] 
Contents, 
Page 
Law LEPOCUCLONy REMAKES). ..crsccsedsnnyosssasseseecsscesccesceetaracsese 936 
Iie dhe EHistory-orihe! Genuses.a.reaaescrscoreaces reeeae a teee eee 937 
iii. The adult Sergestes and Mastigopus ......ccsccsccsscescceceeceees 941 
iv. Synonymical and other Remarks ..............cseceeseceeeeeeeees 946 
v. Gonspectus of the Species © 0.5. 2.....c2ssccssanscacscsarecescostaere 948 
vi. ‘Notes on the Species of Group DL. ..5......s.s0cscccescsccaccseccee 951 
vii. Notes on the Species of Group I1............csccsccsscscoosseecoes 959 
viii. Remarks on Sctacaris and Petalidium of Bate............00600- 967 
ix, Geographical and Bathymetrical Distribution .............000+: 968 
i. Introductory Remarks. 
Three years ago the Rey. T. R. R. Stebbing, in his most useful 
book “A History of Crustacea. Recent Malacostraca” (‘The 
Intern. Scient. Ser. vol. Ixxiv.), writes on the genus Sergestes :— 
“The species known as adults are very numerous, of very various 
BUZOR che cbl'e.s The account of the genus occupies eighty-eight quarto 
pages and seventeen plates of Spence Bate’s ‘ Report on the 
Challenger Macrura.’ It was the subject of a monograph by 
Kroyer in 1856, and the interest of the subject seems still very 
far from being exhausted.” That the supposition in the last line 
of this quotation is correct will be proved by this little treatise. 
Besides the large section of Bate’s ‘Challenger Macrura’ and 
Kréyer’s monograph, almost a score of papers contain contributions 
to the knowledge of this interesting genus; but for all that no 
other group or extensive genus of Decapoda has been up to this 
time so incompletely studied. This will be plainly recognized when 
the chief results of this paper are stated—these are that of the 59 
(07 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 portion are larval stayes 
of species already established on adult specimens, while of the 20 species 
founded on adult specimens 2 with good reason will be excluded 
and at least 4 must be cancelled as synonyms! The authors, who 
have established new species and have avoided describing or at 
least acknowledging larve as real adult species, only make mention 
of large or very large specimens and, in all probability, have not 
studied smaller forms. 
To throw some light upon the older larval stages of the species, 
distinguishing between the larve and the adults, referring a series 
of the larve to the adult forms, examining the value and variation 
of different characters, &c., will be the aim of this short treatise, 
? Communicated by the Rev. T. R. R. Srupsrne, 
