120 THE VOYAGE OE H.M.S. CHALLENGER. 



poid in shape. These animals are very widely distributed, and often occur in . great 

 numbers, but it seems doubtful whether all those hitherto observed may not fairly be 

 referred to one species. The forms assigned by Dana to three distinct species are very 

 probably founded upon various stages of development of one only. 



Onccea obtusa, Dana (PL LI. figs. 1-11). 



Antaria obtusa, Dana, Crust. U. S. Expl. Exped. (1852), p. 1230, pi. lxxxvi. figs. 13, a-e. 



,, mediterranean), Claus, Die frei lebenden Copepoden (1863), p. 159, pi. xxx. figs. 1-7, 

 Onccea venusta (?), Pkilippi, Wiegmann's Arcliiv, 1843, pi. iii. fig. 2. 



„ piriformis, Lubbock, On some Oceanic Entomostraca, &c, Trans. Linn. Soc, vol. xxiiu 

 p. 183, pi. xxix. figs. 24, 25. 



Length, l-20th of an inch (1'3 mm.). Body constricted at the junction of the thorax 

 and abdomen ; conical lenses inconspicuous. Anterior antennas (fig. 4) six -jointed, 

 nearly equally thick throughout, not half as long as the first body-segment ; third joint 

 much the longest, and exceeding in length the last three joints ; last joint of the posterior 

 antennas (fig. 5) small and armed with two fascicles of curved setse ; basal joint with one 

 apical seta. Mouth-organs minute ; mandibles (fig. 6, a) armed at the apex with several 

 laciniated teeth ; maxilla (fig. 6, b) with six or seven slender spine-like setse ; anterior 

 foot-jaws (fig. 7) divided into two stout terminal spine-like processes, which are profusely 

 pectinated on the inner margin, also one slender naked seta ; posterior foot-jaw forming 

 a strongly clawed prehensile hand, which in the female (fig. 8) is elongated, tapering, and 

 bears on the inner margin two stout setse and a series of fine short hairs ; terminal claw 

 stout, falciform ; in the male (fig. 9) the hand is broadly ovate, destitute of long marginal 

 setse, but provided with a continuous series of fine hairs, terminal claw long and rather 

 slender. The swimming feet (figs. 10, 11) have their external and internal branches of 

 nearly equal length, the first two joints being in all cases much the shortest ; marginal 

 spines long, dagger-shaped, with finely serrated edges. Fifth pair of feet extremely 

 small, consisting of a minute tubercle armed with one or two small apical setse. First 

 joint of the abdomen in both sexes very large, much longer than all the rest of the ab- 

 dominal segments put together, and in the male having the posterior angles acutely pro- 

 duced ; second, third, and fourth segments of the male extremely short ; caudal stylets in 

 both sexes about thrice as long as broad, each armed with three subequal terminal setse, 

 the longest of which is about half as long as the abdomen, one smaller terminal and one 

 lateral seta. Ovisacs two, borne closely adpressecl to the back of the abdomen, and 

 reaching, when the ova are mature, nearly to its extremity. 



Habitat. — From the following list of localities it will be seen that Onccea obtusa may 

 fairly be called a cosmopolitan species — excepting, perhaps, from this statement the colder 

 waters of the extreme north and south temperate zones. The Mediterranean is the most 

 northerly region in which it has yet been observed, and indeed had it extended into the 



