COPEPODA FROM IFALUK ATOLL 239 



the form recorded above. In the Ifakik collection the species occurs 

 almost exclusively in sand samples taken at various distances from 

 the reef border; the specimen from locality 800 probably also comes 

 from a sandy bottom. 



Genus Parialysus NichoUs, 1941 



The three monotypic genera Tydemanella A. Scott, 1909 (type 

 species T. typica A. Scott, 1909), lalysus Brian, 1927 (type species 

 /. rujus Brian, 1927), and Parialysus NichoUs, 1941 (type species 

 Tydemanella robusta NichoUs, 1941) certainly are closely related. I 

 have not attempted to redefine Parialysus since I have no males of 

 this genus at my disposal. The differences separating the three genera 

 have been tabulated by NichoUs (1941b, p. 90). The two species 

 described by Sewell as Jalysus investigatoris (1940, p. 230, figs. 44, 

 45) and J. proximus (1940, p. 234, fig. 46) differ so completely in 

 setation from our present concept of Tydemanella, lalysus, and 

 Parialysus that the institution of a new genus for their reception seems 

 necessary. It seems probable, as already has been suspected by 

 NichoUs (1945, p. 15), that SeweU has confused the legs in his de- 

 scription of Jalysus investigatoris. Some specimens of P. rohustus 

 occur in the Ifaluk collection and are described below. 



Parialysus rohustus (NichoUs, 1941) 



FiGtiREs 92c-e, 95-97 



Tydemanella robusta NichoUs, 1941, p. 417, fig. 19.— Sewell, 1949, p. 172. 

 Parialysus robusfus.— 'NichoUs, 1941b, pp. 90, 91; 1944a, p. 491; 1945, p. 7, fig. 3B 



Material. — Loc. 592, 2 juv., one a cf cop. stage V, 0.39 mm.; 2 ad. 

 99, 0.47 and 0.68 mm. length. 



Descriptiox. — The male copepodite stage V and the adult female 

 of 0.47 mm. have been described completely; both have been dis- 

 sected and mounted, 



Male copepodite stage V, total length 0.39 mm.; greatest diameter 

 0.20 mm.; length of longest furcal seta 0.33 mm. 



Body strongly and characteristically built, with large, ovoid cephalo- 

 thorax and smaU, short abdomen; proportional length of both regions 

 is 27:10. Body fairly strongly curved, with the result that, in dorsal 

 view, cephalic somite appears too large and remaining somites too 

 smaU. Head and 1st thoracic somite fused, forming huge cephalic 

 somite, twice as long as rest of body. Greatest diameter of body at 

 end of cephalic somite, very broadly rounded anteriorly; posteriorly 

 narro\^ing considerably (fig. 92c). Back, in lateral view, very 

 broadly rounded and curving imperceptibly into small rostrum, 

 separated from head by shallow groove (fig. 92d). Lateral parts of 



