902 THE VOYAGE OF H.M.S. CHALLENGER. 



immature condition in the brephalos, which approaches the Megalopa stage and as yet 

 no signs of the sixth pair of pleopoda are apparent, nor until after the animal has all the 

 pereiopoda in an advanced condition. Jn fact, a continuous advance in the development 

 to this point has not been observed in the Phyllosoma of the Palinuridse. 



The earliest form of Amphion in the collection (PL CXLVI. fig. 1) was taken in the 

 Pacific, and is 5 mm. (0 - 2 in.) in length. It is slender, and much resembles the Zoea 

 of other Macrura, excepting that the eye is pedunculated. 



The carapace is about 2 mm. long, and covers the entire pereion ; it is narrow, being 

 only a little broader than the anterior somites of the pleon, and is anteriorly produced 

 at the fronto-lateral angles to a small tooth, but there is no rostral point visible. 



The pleon is 3 mm. long, and is composed of six somites ; the five anterior are 

 subequal, the first being furnished with a small anteriorly directed tubercle on each side, 

 which I take to represent the pleocleis of the adult ; the sixth somite is equal in length 

 to all the preceding. It gradually narrows and terminates in a gradually widening, 

 broad, ovate, foliaceous, and spatuliform plate, posteriorly fringed with hairs, one on 

 each side of the median line being small, and six exterior to these long. 



The first or cephalic somite is anteriorly produced in the median line, and furnished 

 with a small, round ocellus ; on the upper surface on each side originate the ophthalmo- 

 poda, of which the peduncle is short and the ophthalmus long-ovate, somewhat pyriform 

 in shape, and about 1 mm. long, or about half the length of the carapace. 



The first pair of antennas is about 1 mm. long, and two-jointed ; the first joint, which 

 is extremely long, appears to represent the peduncle ; the second, which is short, represents 

 the flagellum. 



The second pair of antennae is a little longer than the first, and consists of a basal 

 joint that supports two branches, the inner one represents the flagellum, which is uni- 

 articulate, and reaches a little beyond the distal extremity of the first pair, and the 

 outer is the scaphocerite, which is a little shorter than the flagellum, it is narrow at 

 the base, and gradually enlarges distally; the extremity as well as the inner and outer 

 distal margins are fringed with seven or eight long, slender hairs. 



The oral appendages are at a considerable distance from the frontal margin of the 

 cephalon, and implanted posteriorly to a semicircular epistoma. 



The mandibles, which are immediately posterior to the epistoma, and on each side of 

 the oral aperture, are sharply pointed, and do not carry a synaphipod. 



The three pairs of siagnopoda, as far as can be determined by a general examination 

 without dissecting them out, appear to resemble those that will be more fully described 

 in a later stage. 



At about the same distance posteriorly as the mouth is from the anterior margin of 

 the cephalon, the first pair of gnathopoda is situated ; it consists of a short coxa and 

 a long basis, the extremity of which carries the four succeeding joints of the true leg 



