Sir J. Richardson on Siphonognathus. 227 



Intestina simplex, sine versura recth in anum tendens ; dilatatio 

 ventriculi parva. Cceca pylorica nulla nobis detecta. Vesica 

 pneumatica ampla, 



SlPHONOGNATHFS ARGYROPHANES. 



Ill general form this fish approaches Aulostoma, the structure of 

 the head and the tubular elongation of the palate and os hyoides being 

 similar. The body is less compressed, being roundish, but yet with 

 somewhat flattened sides, and a slight tapering towards the anus. 

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

 great length of head is due to the prolongations of the prefrontals, 

 palatines, vomer, nasal, pterygoids, tympanies and hyoid bones, con- 

 stituting a tube terminated by the horizontal opening 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 

 protects 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, producing a lateral gaping when the mouth is 

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

 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 awU 

 shaped proboscis-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 prominent 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 interopercula 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 follov/s the branchiostegous membrane, whose deeply cres- 

 centic distal edge makes no flap at the isthmus to which it is attached. 

 Four slender, moderately long, elastic branchiostegals support the 

 membrane on each side. One specimen, it may be noticed, has only- 

 three branchiostegals on the right side. The gill-plate 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-opening appears, nine-tenths of the opening being below it. 

 No bony crests or spinous points 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* 



