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



is enveloped in soft skin, whicli is thickest and mucigerous on the snont ; no foramina 

 leadincr into the muciferous system can bo distinguished. The nostrils lie immediately 

 in front of the eye. 



The thick end of the snout overlaps the mouth, which is horse-shoe-shaped, its lateral 

 cleft extending to the front margin of the eye. Barbel none. 



The branchial cleft extends from the upper end of the gill-cover far forwards, the 

 branchiostogous membranes being free from each other. Gill-laminte well developed ; 

 sill-rakers rather short, soft, lanceolate. 



All the fins are long-rayed. The dorsal fin has a rather broad base, the length of 

 which is about one-third of its distance from the end of the snout ; it is very high, its 

 longest rays being much longer than the head, and even exceeding the pectoral fin. As 

 regards the anal fin, the rays of its anterior portion are about equal to the depth of the tail, 

 l)ut the posterior increase in length, and exceed ranch the gradually decreasing depth of the 

 tail. The pectorals have a narrow base, are longer than the head, and extend backwards 

 to the origin of the anal. The ventrals consist of two rays each, of which the longer is 

 l)ifid at the end, and nearly reaches the vent ; the shorter and inner is rudimentarj'. 



The fish is nearly transparent, with a brownish tint ; dorsal and pectoral fins and a 

 Iiroad margin of the anal black. 



I am indebted to M. Tegima of the Tokio Museum for a specimen of this extremely 

 rare fish, which does not seem to have been observed since it was described in the 

 Fauna Japonica. It is 9 inches long, and iu a good state of preservation, except for a 

 certain degree of desiccation, which it has undergone in consequence of the action of the 

 spirit on the mucous layer with which it is covered. Our specimen difi"ers in the shape of 

 the fins from the figure given by Schlegel. Perhaps this is due to age, as the specimen 

 of the Dutch naturalist was considerably larger. 



Family P l e u k o \ e c t i d ^.' 



As far as our present knowledge goes, Flat-fishes are, unlike the Gadoids and Oj)lii- 

 dioids, but sparsely reiiresented in the deep sea, and have not yet reached to a deptli of 



' For tlie sake of completene&s I mention liere a small Flat-fish, 72 mm. long, which was obtaineJ by the U.S. Fisli 

 Commission at depths of 8(i and 115 fathoms, in lat. 40° C N., long. 70° 2.3' W., and which ha.s been described by Mr. 

 Brown Ooode under the name of Thxjris or Delothyrii pellucidus (Proe. U.S. Nat. Mus., vol. iii. p. 344, 1880; and p. 1 10, 

 1884), and which both lie and Mr. Jordan regard as a larval form. As generic diagnosis the following description is 

 given : — "A genus of heterosome fl^^hc3, with soft, transparent, elongate body. Head very short (in the single species 

 contained about 5i times in total length of body). Moiitli small, toothless. Eyes upon left side, close together, the 

 lower slightly in advance of the upper. Pectoral fin upon blind side shorter and with fewer rays than upon coloured 

 side. Ventrals crowded together upon median keel of body, their bases prolonged upon this keel. Dorsal fin com- 

 mences in front of the eye upon the snout. Dorsal and anal rays simple. Caudal fin subsessile, almost confluent with 

 dorsal and anal. Scales very small, thin, easily detached. Dorsal line marked, straight. Body translucent, colourless 

 (except for three longitudinal stripes in the single species). The vertebni' can almost be counted through tlie llesh when 

 the fish is held up to the light, and the arrangement of the gills is clearly visible through the opercular bones." 



