Sir J, Richardson on Siphonognathus. 227 



Iitfrsfiiia sii/iphw, sine versura rectb in anum tendens ; dihttatio 

 ventriculi parva. C<eca pylorica nulla nobis detecta. Vesica 

 pneuinatica amplu. 



SllMIONOGNATHTTS ARGYROPHANES. 



In s;cncrnl form this fish appronclics Aulostoma, the structure of 

 tho head and thi" tuhuhir c'h)n<;ation of the pahxte and os liyoidcs being 

 similar. Tlie body is loss compresst-d, \w\\v^ roundish, but yet with 

 somewhat tlattcned sides, and a slii>ht tapering towards the anus. 

 The compression increases in the tapering tail. As in Aulostoma, the 

 great length of head is due to the ])rolongations of the prefrontals, 

 palatines, vomer, nasal, pterygoids, tymi)anics and hyoid bones, con- 

 stituting a tube terminated by the horizontal oj)ening of the mouth. 

 The premaxillaries form the upper border of the mouth, and have 

 little or no motion. They conceal the slender limb of the maxillary, 

 but the irregularly triangular or small suborbicular plate of the latter 

 ])rotects the corner of the mouth. Equal in length to the maxillaries, 

 the mandible is articulated to the extremities of the tympanies, and 

 is slightly curved, ])roducing a lateral gaping when the mouth is 

 closed. Both it and the premaxillaries are edged by narrow lip3 

 which fold back on the limbs of their respective bones. At the ex- 

 tremity of the snout the premaxillary lips unite to form a fine awl- 

 shaped ])roboscis-like barbel, which hangs down before the mouth. 

 No teeth whatever could be discovered in the jaws or in the tubular 

 mouth, — not even in the pharynx, which is narrow. Form of the head 

 a slender four-sided obelisk, the space between the eyes being occu- 

 pied by the forked mid-frontal, into which the nasal is dovetailed. 

 The latter as it runs forwards is feebly convex, and shows a smooth 

 and scarcely jirominent medial line, which terminates in the slightly 

 swelling extremity of the bone and of the snout. Under each edge 

 of the nasal, the long slender premaxillary appears as already men- 

 tioned. On the sides, the facial tube is completed by dark brown 

 membrane, and on the ventral surface also a membrane stretches 

 from the interojiercula and tympanies of one side to those of the 

 other, being supported on the mesial line, interiorly by a very slen- 

 der lingual bone, which is neither prominent nor covered with flesh 

 so as to form a tongue. Continuous with this under-surface of the 

 mouth follows the branchiostegous membrane, whose deeply cres- 

 eentic distal edge makes no flaj) at the isthmus to which it is attached. 

 Tour slender, moderately long, elastic branchiostegals support the 

 meml)rane on each side. One specimen, it may be noticed, has only 

 three branchiostegals on the right side. The gill-})late is connected 

 to the nuchal region by scaly membrane, and terminates in a small 

 flexible strap- shaped apex, above which only a small corner of the 

 gill-opeuing appears, nine-tenths of the opening being below it. 

 No bony crests or spinous j)oints exist on the cranium. The nostrils 

 are on the edge of the head, close before the eye, the hinder one being 

 an open pore, not above a line from the orbit, and the other is situated 

 a quarter of an inch before it in a pulpy membrane, and being closed 



15* 



