NO. 1573. PA RASITIC COPEPODS— WILSON. 377 



come from a broad survey and comparison of all the known genera 

 and species. » 



But even with these advantages the recent writers have still 

 failed to recognize the structures behind the genital segment as a 

 sixth thorax segment with its dorsal plates and rudimentary swim- 

 ming legs. These structures are plainly marked here in Dinematura, 

 but are rudimentary or even lacking in the other genera. They are, 

 of course, morphologically the same in all the genera, however 

 rudimentary they may be, but have been very differently regarded 

 by different investigators. 



For instance, the dorsal process has been considered a process of 

 the genital segment in the present genus, as the first segment of the 

 abdomen in Pandarus and GangliopuSj as a foliaceous dorsal lamina 

 of the abdomen in Demoleus, while it has been wholly overlooked in 

 Laminifera and EcJdhrogaleus , in both of which, however, it exists 

 and can be easily found. 



One of the most recent investigators, Bassett-Smith, in his Enu- 

 meration of the Known Species of Parasitic Copepods (1S99), describes 

 this sixth segment as " a small median process (of the genital segment) 

 partially covered by two narrow plates" (p. 463), while he regards 

 the rudimentary swimming legs upon its ventral surface as lateral 

 processes of the abdomen. But as soon as we realize that this is really 

 a sixth segment we have recognized the most important characteristic 

 of the genus Dinematura. and one which will certainly distinguish it 

 from all its relatives. This has been indicated in the diagnosis given 

 above by the use of italics. 



DINEMATURA FEROX Kroyer. 



Plate XXII. 



Dinematura fcrox Kroyer, 1838, p. 40, pi. i, fig. 5. —Milne Edwards, 1840, 



p. 465.— Steenstrup and Lutken, 1861, pp. 376, 379, pi. vii, fig. 14. 

 Dinematura carcharodonti Thomson, 1889, p. 360, pi. xxvi, fig. 2. 



Female. — Body three times as long as wide, both the carapace and 

 genital segment thick and strongly arched. Carapace, including the 

 posterior lobes, nearly orbicular; lateral areas narrow, their trans- 

 verse suture just in front of the posterior margin of the carapace, and 

 forming a well-defined notch on each lateral margin; posterior lobes 

 long, conical, and curved inward at their tips. Frontal plates very 

 narrow and insignificant; median incision scarcely visible; eyes 

 small and about one-third the distance from the anterior margin. 

 The three free thorax segments about the same length, but dimin- 

 ishing regularly in width backward. Lateral plates on the second 

 segment reaching back to and overlapping the plates on the fourth 

 segment. No dorsal plates on the third segment; those on the fourth 

 segment short and narrow, the same width as the genital segment and 



