REPORT ON THE DEEP-SEA FISHES. 213 



an enormous gape wliich extends backwards beyond the base of the pectoral fins. On 

 the other hand, the gill-cover is still more reduced than in the other Stomiatids, and 

 quite rudimentary. 



A perfectly unique structure is a thin, cylindrical, muscular band which connects the 

 back part of the mandiljulary symphysis with the extremity of the hyoid bone. It is 

 probably the homologue of a muscular band which in other Stomiatids stretches on each 

 side from the mandible to the side of the hyoid, the two bands coalescing into an un- 

 paired one in Malacosteus. It is, in the present state of preservation, much elongate, 

 like a barbel, but during life it is probably contractile and serves to give to the extremity 

 of the mandible the requisite power of resistance when the fish has seized its prey, as 

 without such a contrivance, so long and slender a bone would yield to the force of its 

 struggling victim. This structure is so unique, and the band so similar to a barbel 

 that, before having become acquainted with it by autopsy, I imagined that its original 

 describer. Dr. Ayres, had misunderstood its character, and that he had only seen a 

 barbel like that of Stomias or Echiostoma. Dr. Ayres had not made any suggestion as to 

 its probable function. 



Being provided with a mouth which allows of the passage of fishes much exceeding 

 in size its own bulk, Malacosteus must have as distensible a stomach as Chiasmodus or 

 Omosiidis. Both the specimens which are known had the stomach empty, but in 

 our example the integuments of the abdomen are so distinctly longitudinally folded that 

 there can lie no doubt on this point ; and probably Stomias and Pachystomias are 

 likewise able to swallow large fishes, though this peculiarity is less developed in them 

 than in Malacosteus. 



The eye is comparatively large ; and it would be quite inconceivable that a fish 

 living at a depth to which no ray of the sun can penetrate, should be provided with an 

 organ of sight so much developed, unless light be produced from some other source or by 

 the fish itself In Malacosteus the subocular luminous organ ^ is broken up into two bodies 

 imbedded in the muscular substance ; the anterior is the larger, pear-shaped, with the 

 narrow end directed forwards and wedged into the narrow space between the eye and 

 intermaxillary; the posterior is situated somewhat further back, above the maxillary, 

 smaller and of a more rounded form. Both are now of the colour of a crystalline 

 lens after immersion in spirit, and surrounded by a very narrow pearly ring. 



Small eye-like organs are arranged in longitudinal series along the lower part of the 

 side, and scattered between the series; others are scattered over the ujsper parts, but 

 owing to the state of the specimen I am unable to trace the series in their whole course 

 or to ascertain their number. 



The gills are four in number with very short laminae, and without gill-rakers; of 

 branchiostegals I counted eight, aU extremely short, rod-like and cartilaginous. 



1 Its histological structure will be described ia Appendix B. 



