this species found in a given geographical 

 range. As the hosts of this parasitic copepod 

 are mostly inshore fishes and not powerful 

 swimmers, considerable distant movement 

 probably is accomplished only by drifting with 

 the current. At present, however, it is impos- 

 sible to determine whether the Gulf Stream has 

 influenced this picture of geographical varia- 

 tion. 



The single specimen of T. imipressns de- 

 scribed by Krdyer (1837) is a female taken 

 from the inner surface of the pectoral fin of a 

 Diodon hystrix in the Danish West Indies. It 

 definitely belongs to the Caribbean type, since 

 in Kroyer's fig. 2a (dorsal view) and fig. 2b 

 (lateral view) the posterior lobes, anterior 

 lobes, and the bilobed condition in the head are 

 of that type. According to Kroyer's description 

 (p. 479) this Danish West Indian specimen 

 measures 2 lines, of which the egg sac is about 

 half. In other words, the length of the para- 

 site's body is about 2.11 mm., which falls within 

 the range of the Caribbean type (see table 6). 



The 37 specimens of T. impresses described 

 by Carvalho (1951) from Brazilian C. schoepfi 

 measure from 1.52 to 1.80 mm., and so fall with- 

 in the range of the Caribbean type. 



In his discussion of the validity of Nord- 

 mann's T. impressus, Wilson (1911: 359) ex- 

 pressed his doubt upon the variation of the 

 specimens of T. impressus: "either Nordmann's 

 species or that of the present author is new to 

 science. They can not both be identical with 

 Kroyer's T. impressus." This implies that Wil- 

 son's specimens are different from Kroyer's 

 T. irnpressiis to a certain degree, but this dif- 

 ference is not as significant as the discrepancy 

 between Krdyer's T. impressus and Nord- 

 mann's T. impressus. Consequently, Wilson 

 identified his specimens collected in Beaufort, 

 N.C., as T. impressus, and created T. verru- 

 C0S7IS for Nordmann's T. impressus. 



The total length (1.67 mm.) given by Wilson 

 (1911: 356) for the species of T. impressus is 

 too small for the Atlantic type. I have measured 

 all 30 specimens that were identified by Wilson 

 as T. impressus in USNM collections. The col- 

 lections, number of specimens, and maximum 

 sizes are : 



It is obvious, therefore, that Wilson took into 

 consideration only the specimens in USNM 

 38625. This collection unfortunately contains 

 no fully grown ovigerous females (judged by 

 the length of the egg sac). One of the three 

 immature adult females in this collection was 

 described by Wilson as a male, and the meas- 

 urements given for it are (Wilson, 1911 : 357) : 



Total length, 1.27 mm.; cephalothorax, 0.3 

 by 0.5 mm. ; trunk 0.75 by 0.51 mm. ; and width 

 of genital segment, 0.25 mm. 



Thest; figures lie within the range of the im- 

 mature adult female with a longer (guitar- 

 shaped) trunk given in table 2. 



The 10 specimens of T. impressus reported 

 by Nordmann (1864) were taken from a 

 "fleckigen Diodon-Art." According to Nord- 

 mann's description on p. 491, these parasites 

 measure about 5 mm. long including the egg 

 sac. Judging from his illustration of a complete 

 parasite in pi. VI, fig. 7, the body is about 3.15 

 mm. long and the egg sac, 1.85 mm. ; therefore, 

 the size is about that of the Atlantic type of the 

 T. impressus. According to what Nordmann 

 described (pp. 491-494) and illustrated (pi. 

 VI, figs. 7-10), however, this West African 

 species of Tucca is definitely different from all 

 three types of T. impressus in the North and 

 South American waters. 



ACKNOWLEDGMENTS 



Two field collections and the subsequent 

 laboratory study have been aided by a grant 

 (GB-1809) from the National Science Founda- 

 tion of the United States to Arthur G. Humes, 

 who also critically reviewed the first draft of 

 this report. Roger F. Cressey, Division of 

 Crustacea, U.S. National Museum, Washington, 

 D.C., loaned the USNM collections of the speci- 

 mens of Tucca i7npressus Kroyer; W. Ver- 

 voort, Rijksmuseum Van Naturlijke Historie, 

 Leiden, The Netherlands, and P. Illg, Uni- 

 versity of Washington, Friday Harbor, Wash., 

 reviewed the manuscript, as did Kenneth Sher- 



CYCLOPOID COPEPODS OF GENUS TUCCA 



297 



