No.no^. PARASITIC COPEPODS—CALIGID.E— WILSON. 555 



GENUS CALIGUS Muller. 



Carapace large, shield-shaped. Basal joints of the first antenna? 

 provided with lunules; two terminal joints free, heavily armed with 

 setjB. Mandibles often toothed along both margins. Second maxilla? 

 simple, spine-like. First and fourth thoracic legs uniramose, second 

 and third bi ramose. Fourth thorax segment without dorsal plates; 

 genital segment simple also, without plates or processes. A})domen 

 one to many segmented. The young of both sexes with a frontal lila- 

 ment for attachment during the chalinnis stage. Anal lamelhe strongly 

 flattened and armed with long plumose seta?. 



{Callgo^ obscurity, darkness.) 



AKTIFIt'IAL KEY TO THE SPECIPiS. 



The relative length of the different ]x)dy regions is the most ('onstant character 

 available for classification of species. 



Both sexes are here included, since they usually exhibit radical differences, and 

 they must be sexually mature, although the presence of egg strings in the female is 

 not necessary. When the fifth legs are spoken of as visiljle or invisible it means in 

 dorsal view only, and has no reference to a microscopical examination of the ventral 

 surface. All measurements of length include the anal lamella', but not the plumose 

 seta? upon them. Differences of length must amount to eight per cent or ten per 

 cent; otherwise they are considered as "about equal." In any case where there 

 might still be danger of mistake after this liberal allowance the species has been 

 inserted twice. This key includes all valid species known at the present time. The 

 authority for each species is here given, and the reference can be found in the biblio- 

 graphy on p. 666. 



There have been eliminated the following species: 



Fird, those which subsequent examination has shown to belong to other genera. 

 Here are included bicolor (Lamarck, 1818), which is a Pandarvs; branrhialis (Steen- 

 strup and Liitken, 1861), a Lepeophtheirus; breripedis (B-Smith, 1896), a PseudocuUgus; 

 crassus (Abildgaard, 1794), an Anthosoma; gracilis (v. Beneden, 1851), hippoglossi 

 (Kroyer, 1837), molvse. (Latreille, 1825), nordmannii (M-Ed wards, 1840), obscurus 

 (Baird, 1850), ornatus (Nordmann, 1832), pacificus (Gissler, 1883), pedoralis (Midler, 

 1785), pharaonis (Nordmann, 1832), salmoiiis (Kroyer, 1837), slurionis (Kroyer, 1837), 

 stroma (Baird, 1850), and vespa (M-Ed wards, 1840), all of which belong to the genus 

 Lepeophtheirus. Imbricatus (Risso, 1816) is an Anthosoma; oblongus (Abildgaard, 1794) 

 is a Dichelestium; paradoxus (Otto, 1828) is a Deinoleus, and smithii (Lamarck, 1818) 

 is an Anthosoma. 



Second, those which have proved to be synonyms of species already described. 

 Here are included seglefini (Kroyer, 1863), a male curtus; arnericanus (Pickering and 

 Dana, 1838), also a curtus; bengoensis (T. Scott, 1894), a young male coryphsense; 

 bicuspidatus (Nordmann, 1832), a curtus; carangis (Kri^yer, 1863), an alalongse; 

 diaphanus (Baird, 1850), a curtus; elegaus (v. Beneden, 1851), a curtus; elongatus 

 (Nordmann, 1832), a rapax; leptochilus (Leuckart, 1847), also a rapax; longicaudus 

 (B-Smith, 1898, a), a trichiuri; nudleri {Leach, 1816), a curtus; scombri (B-Smith, 1896) , 

 a produclus; rissonianus (M-Edwards, 1840), a curtus; scutatus (M-Ed\vards, 1840), a 

 corypha.'ns'. 



Third, forms of which no figure has ever been published and which were so poorly 

 described as to make their identification impossible. Here are included affinis 

 (Heller, 1866), put into the key provisionally; kroyerii (M-Ed\vards, IMO) , piscinus 



