52 THE VOYAGE OF H.M.S. CHALLENGES. 



were many of its parts so carefully observed as they ought to have been, as at the time I 

 did not suspect that I should not be able to lay my hands on another specimen. The 

 whole gathering, however, which is remarkably poor in Copepoda, has been hunted over 

 without success, for further examples. The length of the anterior antenna is half an inch 

 (1275 mm.), and is probably about the same as that of the body of the animal. 



Undina, Dana. 



Unclina, Dana, Proc. Amer. Acad. Sci., 1849 (not Undina of Claus). 



Head anchylosed with the first thoracic segment. Anterior antennae twenty-five- 1 

 jointed in the female ; those of the male alike on both sides, twenty -two to twenty-four- 

 jointed, not geniculated, but distinctly angulated at the sixth or eighth joint. Both 

 branches of the posterior antennae equal in length, secondary branch four-jointed, the two 

 median joints very short and indistinct. Mandible broad, numerously toothed, palp with 

 a large quadrate base and two short bi-articulate branches, the first joint of the inner 

 branch swollen and almost circular. Maxilla-palp well developed, the lower branch 

 digitiform, three-jointed, the upper smaller and crescentic. Anterior and posterior foot- 

 jaws as in Calanus. Five pairs of feet in both sexes, both branches three-jointed ; fifth 

 pair in the male on the right side very largely developed and prehensile, on the left 

 small and not much different from the preceding pairs. Abdomen of the male five-, of the 

 female four-jointed. 



The angulated male antenna, the three-jointed inner branches of all the swimming 

 feet, the absence of excessively long antennal and caudal setse, the prehensile form of only 

 one of the fifth feet in the male, and the presence of five pairs of feet in the female, are 

 the characters which distinguish Undina from the very closely allied genus Euchceta. 

 From Scolecithrix it is separated by the larger number of joints in the anterior antenna, 

 the equality of the two branches of the posterior antenna, the uniformly three-jointed 

 inner branches of the swimming feet, and the presence of a normally formed fifth pair 

 in the female, while Scolecithrix is still further distinguished by the peculiarity from 

 which it takes its name — the presence of a fascicle of worm-like filaments at the apex 

 of the posterior foot-jaw. Both the species here described have a very wide range of 

 distribution, being found abundantly over almost the whole areas of the Pacific and 

 Indian Oceans, and over a large part, at any rate, of the Atlantic. Undina messinensis, 

 Claus, and Undina dance, Lubbock, present some peculiarities of structure which have 

 led me to place them under a distinct genus (Scolecithrix), and Undina ptdchra, Lubbock, 

 seems properly to belong to Euchceta. 



