34 PROCEEDINGS OF THE NATIONAL MUSEUM ^ol. 121 



endopod unmodified. Abdomen 2-segmented. Caudal rami attached 

 distally to abdomen. . . 



Discussion.— This genus is represented by two species, Ferissopus 

 dentatus Steenstrup and Liitken 1861 and P. ohlongatus (WHson, 1908) 

 A discussion of the history of the synonomy of these species is mcluded 

 in the species descriptions. 



Perissopus ohlongatus (Wilson, 1908) 



Achtheinus ohlongatus Wilson, 1908, p. 450. 

 Achtheinus dentatus Wilson, 1911, p. 630. 

 Achtheinus pinguis Wilson, 1912, p. 235. 

 Achtheinus japonicus Wilson, 1922, p. 4. 

 Achtheinus parvideus Wilson, 1923, p. 7. 

 Achtheinus intermedius Kurtz, 1924, p. 614. 

 Achtheinus galeorhini Yamaguti, 1936, p. 11. 

 Achtheinus platensis Thomsen, 1949, p. 20. 

 Achtheinus chinesis Thomsen, 1949, p. 23. 

 Achtheinus impenderus Shen and Wang, 1958, p. 27. 



Discussion.— In 1908 Wilson described a new copepod and erected 

 for it a new genus, Achtheinus. Smce then, 10 species assigned to this 

 genus have been described. A comparison of the description and 

 figures of these species show that they should be included m the genus 

 Perissopus. This is apparent when one compares the appendages of 

 the two groups. In both, the second antenna has a hoodlike process 

 bearinc^ spines. The maxillipeds of each bears a reduced claw and the 

 basal s^'egment is in the form of a flattened pad. Legs 1-4 are much 

 reduced in both and are smiilar in form. 



I have grouped all species described in the genus Achtheinus as 

 one species. These had been separated on the basis of overall form 

 and not on details of the appendages. It is apparent that we have 

 here a situation like that found in Perissopus dentatus— & single species 

 with variation in body form. I have examined WHson's material of 

 A ohlongatus, A. dentatus, and A. pinguis, and I could find no good 

 basis for keeping them as separate species. On the basis of the 

 descriptions of other species, there is no valid evidence to justify 

 more than one species. Probably the best description of the ap- 

 pendages of this species can be found in Yamaguti's (1936) description 



of A. galeorhini. i ■■ • to 



This species can be separated from P. dentatus on the basis ot z 

 characters. In P. dentatus the posterior corners of the genital seg- 

 ment are sharply angular whereas in P. ohlongatus they are rounded. 

 In P. dentatus the endopods of legs 1-4 are unarmed. In P. oh- 

 longatus the endopods of legs 1 and 2 and sometimes 3 are armed 

 with short setae. 



I did not collect this copepod and more material would certainly 



