SHEATFISII. 



6!l5 



bivadtli lit' llic intei'orhital spare, and also only a little 

 more than 14 % of the length of the snout. As appears 

 from thes(> nieasurenients, the; breadth of the low, hut 

 rounded interoi'liital space measures about ' \, (varying, 

 lio\ve\er, between .")") and 48 %) of the length of the 

 head, and the length of the snout usually a little more 

 than ' :, (varying Ijetweeu 88 and ?i?i %) of tiie same 

 length. Here, however, as usual, the length of the snout 

 is measured obliquel)' (from the anterior margin of the 

 eyes to the middle of the tip of the snout): its real 

 leno-tli (the distance between its tip and the middle of 

 the line joining the anterior margins of the eyes) is 

 in \onng specimens rather more than ' ,, in specimens 

 1 m. long rather less than \ o, and in our largest spe- 

 cimen ai)out " - of the Ijreadth of the interorbital s]«ice. 

 In projiortion to the entire length of the head the real 

 length of the snout decreases, during the growth of the 

 fish from a size of 3 dm. to one of 2 m., from '/^ to 

 onlv ' -, of the said length of the head, and at the same 

 time from ai)out 41 to 28 % of the postorbital length 

 of the head. The eyes thus lie invariably in the fore- 

 most third of the head, just behind the line between the 

 liiud margins of the corners of the mouth. Just in front 

 of this line, or exactly in it, lie the posterior pair of 

 nostrils. Tliese nostrils are small and round, -and are 

 situated so far inwards that the distance between them, 

 which is relatively less in old specimens, measui-es only 

 about (i6 — .')6 ?6 of the breadth of the interorbital space. 

 The anterior jiair of nostrils lie far out on the snout, 

 in the line between the maxillary barbels, and at a 

 somewhat smaller distance from each other. The margin 

 of all the nostrils is tubular, the posterior pair being 

 more elevated in a funnel-shape. 



Of each of the maxillarj- bones there remains, as 

 we have indicated above, hardly more than the articular 

 knob itself, a small, triangular or scaphoid bone, hollow 

 on the outside and articulating on the inside, which is 

 button-shaped, with the lateral ethmoid (prefrontal) bone 

 and the intermaxillar)' bone. But on the lower anterior 

 side of this bone we find another, still smaller, supple- 

 mentary bone, forming the base of the maxillary barbel, 

 which is long and narrow, but compressed, and may be 

 moved in all directions. The length of this barbel is, 

 however, extremely variable. Now and then the barbel 

 on one side of the body differs from that on the other. 

 As a rule too, these barbels are comparativeh- shorter 

 in old specimens than in young: in a specimen 1 metre 

 long the longest barbel measured somewhat more than 



Scamlinavinn Fishes. 



■',',„ of the lengtii of the bod\', in a specimen 2 metises 

 long not ([uite '/,. of the same Unigth or, in other words, 

 a little more tiian the lengtii (jf the head. The two 

 ])airs of barlx'ls on tlie lower jaw ai'e considerably shorter, 

 the anterior pair being also shorter than the posterior, 

 which generally extend to aljout a line with the hind 

 margin of the preopei'culum or with tlH> articulation of 

 the o[)erculum. These barbels are not set on the lower 

 jaw itself, but a little farther inwards, on the skin be- 

 tween the branches of the ja\v, the anterior pair nearly 

 below the anterior nostrils, the posterior pair below 

 the anterior uuirgins of the ej'es. 



The surface of the head is smooth, and the bones 

 and cavities which other\vise give many Glanomorphs 

 one or mori' important diaracters, are perceptible only 

 to the touch. Within this series of families we rather 

 constantly find, in the forms that have a more or less 

 fully armoui'ed head, a longitudinal groove, or an oblong, 

 naked patch, along the middle of the forehead and snout. 

 Here, as in the other forms the head of which is des- 

 titute of dermal ossifications, no groove of this kind is 

 externally perceptible; but in the skull we find a long 

 opening (fontanel) between the anterior parts of the 

 frontal bones proper, and this opening is continued 

 bet\veen the posterior parts of the ethmoid bone. 



In the same way we find no external trace of the 

 suborbital ring; but in the skeleton it displays some 

 striking peculiarities. The foi-emost bone in this ring 

 (the preorbital bone) is comparatively small, flat, tri- 

 angular, and acute-angled in front. One side of this 

 bone lies on the outer top of the lateral ethmoid bone, 

 and the point in front is united by ligaments to the 

 top of the long lateral process of the ethmoid bone 

 proper. With its inside this l)one forms the outer mar- 

 gin of the nasal cavity, the inner margin of which is 

 formed by the long, but also fairly broad nasal bone with 

 its somewhat crescent-like shape. Both the nasal bone 

 and the preorbital bone are furnished on their upper 

 surface with hollows and grooves for the ramifications 

 (muciferous ducts) of the lateral line. The second sub- 

 orbital bone forms the anterior margin of the orbit and 

 occupies a singular position, straight outwards and down- 

 wards from the lateral ethmoid bone, while its length 

 is so great that the tip lies above the lower jaw, though 

 without coalescing with the latter, just in front of the 

 articulation thereof. At the distal part of this sub- 

 orbital bone, with its anterior side united to the pos- 

 terior side thereof, lies the third suborbital bone, which 



