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Show 936 DR. H. .T HANSEN ON CRUSTACEANS [Dec. 1, 6. On the Development and the Species of the Crustaceans of the Genus Sergestes. By Dr. H. J. H A N S E N (Copenhagen) 1. [Received October 15, 1896.] CONTENTS. Page i. Introductory Remarks 936 ii. The History of the Genus 937 iii. The adult Sergestes and Mastigopus 941 iv. Synonymical and other Remarks 946 v. Conspectus of the Species 948 vi. Notes on the Species of Group 1 951 vii. Notes on the Species of Group II 959 viii. Remarks on Sciacaris and Petalidium of Bate 967 ix. Geographical and Bathymetrical Distribution 968 i. Introductory Remarks. Three years ago the Rev. T. R. R. Stebbing, in his most useful book " A History of Crustacea. Recent Malacostraca" (The Intern. Scient. Ser. vol. lxxiv.), writes on the genus Sergestes:- " The species known as adults are very numerous, of very various sizes 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 tbe 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 Kroyer'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 (or 60) hitherto described species only about 20, or one-third of the 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 larvae, and even of these a considerable portion are larval stages 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 larvae 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 larvae and the adults, referring a series of the larvae to the adult forms, examining the value and variation of different characters, & c , will be the aim of this short treatise. 1 Communicated by the Rev. T. R. R. STEBBING. |
