AHT.5. NORTH AMERICAN PARASITIC COPEPODS WILSON. 21 



11. Abdomen very short ; rami of swimming legs three-jointed ; anterior thorax 



segments longer and wider than posterior ones. 



Donusa Nordmann, 1864, p. 72 



12. First three pairs of legs mere stumps; fourth pair with two short unseg- 



mented rami Bassettithia, new genus name, p. 72 



12. First two pairs of legs biramose, rami two-jointed; last two pairs mere 

 stumps without rami Pseudoclavella Basset-Smith, 1898, p. 73 



12. First and third pairs of legs uniramose, unsegmented ; second pair biramose, 



rami unsegmented ; fourth pair mere stumps without rami. 



Pseudocycnus Heller, 1865, p. 74 



13. First two pairs of legs biramose, rami two-jointed ; third and fourth pairs 

 wanting or reduced to setae ; second antennae uncinate. 



Hatschekia Poche, 1902, p. 81 

 13. First Pwo pairs of legs biramose, rami one-jointed; third pair lamellar; 

 fourth pair lacking ; second antennae chelate. 



Dichelesthium Hermann, 1804, p. 85 



13. First legs biramose, rami one-jointed ; second pair uniramose ; third pair 



mere stumps without rami ; fourth pair lacking ; second antennae large but 



not chelate CyUcola Basset-Smith, 189S, p. 88 



13. First legs biramose, rami two-jointed ; second and third pairs uniramose, 

 rami one-jointed ; fourth pair lacking ; second antennae with setae only, no 

 chela or claw Veiitriculina Basset-Smith, 1903, p. 89 



Rejected genera. — In 1837 Kr0yer published ^ the description of a 

 new species of parasitic copepod, which he named Aefhon quadratus. 

 It was founded on a single specimen taken from the gills of a West 

 Indian Sen-anus. For discussion of this genus see p. 30. 



In I860® Lubbock described and figured a new species which he 

 called Baculus elongatus. He said that it resembled the Caligidae 

 more than the Dichelesthiidae, to which its long antennae would ally 

 it. It has since been proved to be a stage in the development of Pen- 

 nella, and hence becomes a Lernaean. 



The genus CJaveJla is rightly a Lernaeopod, as was explained ' 

 but it has been used by many authors to designate species belonging 

 to the present family. To obviate the difficulty of having the same 

 genus in two different families Poche suggested the name IlaUchekla. 

 for such species as belong to the Dichelesthiidae, and for these species 

 the name Clavella becomes a synonym. 



A genus called Cycnus was established by Milne Edwards^ to in- 

 clude a single species, but the name had already been used by Hube- 

 ner for a genus of Lepidoptera in 1816 and hence cannot be retained 

 for the copepod genus. In 1854 P. J. van Beneden described a genus 

 and species which he claimed as new and to which he gave the name 

 Congencola pallida.^ This has proved to be the same generically as 

 Milne Edwards's specimens, but differs from them specifically. Ac- 



» Naturhistorisk Tidsskrift, vol. 1, p. 257, pi. 2, flg. 9 ; pi. 3, fig. 1 Or-o. 



• Trans. Llnnaean Soc, vol. 23, 1860, p. 190, pi. 29, figs. 40 and 42. 



' Proc. U. S. Nat Mus., vol. 47, 1915, p. 666. 



' Histoire Naturelle des Crustacea, vol. 3, 1840, p. 495. 



» Bulletin Acad, de Belgique, vol. 21, pt 2, p. 583, 



