936 Bii. n. .T HANSBir on crustacbanb [Dec. 1, 



6. On the Development and the Species of the Crustaceans 

 of tlie Grenus Sergestes. By Dr. H. J. Hansen (Copen- 

 hagen)'. 



[ReceiTed October 15, 1806.] 



Contents. 



Page 



i. Introductory Remarks 936 



ii. TLe History of the Genua 937 



iii. 'i:\\e aAuXt Sergestes vinA Mastic/opus 941 



iv. Synonymical and other Remarks 946 



T. Oonspeetus of the Species 948 



vi. Notes on the Species of Group 1 951 



vii. Notes on the Species of Group II O.'jO 



Tiii. Remarks on Sciacaris rniHt. I'etalidium oi ^Ate 967 



ix, Geogrupliical and Batliymetrical Distribution 908 



i. Introductory Remarhs. 



Three years ago the Rev. T. E. E. Stebbing, in his most useful 

 book " A History of Crustacea, llecent Malacostraca " (The 

 Intern. Scient. Ser. vol. Ixxiv.), 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 fcSpence Bate's ' Eeport on tlie 

 Challenger Macrura.' It was the subject of a monogra])li by 

 Kriiyer in 1856, and the interest of the subject seems still very 

 far from being e:^hausted." That the supposition in the last line 

 of this quotation is correct will be proved by this Uttle treatise. 

 Besides the large section of Bate's ' Challenger Macrura ' aud 

 Kroyer's monograph, almost a score of papers contain contributions 

 to the laiowledge of this interesting genus ; but for all that no 

 otlier group or extensive geiuis of Docapoda has been up to tins 

 time so incompletely studied. This will be plainly recognized when 

 the chief results of this paper are stated — these are that of the 5t) 

 {or 60) hitherto described species only ahout 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 larvw, and even of these a considerable portion are larval stages 

 of species already established on adult specime^is, ivhile of the 20 species 

 founded on adult specimens 2 with good reason ivill 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 larvo) as real adult species, only make mention 

 of large or very large specimens aud, 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 larvte to the adult forms, examining the value and variation 

 of different characters, &c., will be the aim of this short treatise. 



' Oommunicated by the Rev. T. R. R. Stebbing. 



