TlIlfKK-Sl'lNKl) STI('K1,E1!ACK. 



(;-)i 



well as tlu; "tlicr [ilMtcs mikI Ixjucs tli;it Mjipcar ill the 

 stirt'are of tlic body, arc rouiili witli <;rou\<;s altei'iiatiug' 

 with i;Taiiuliito(l rulnrfs, coiTcspoiuliiio; to tlie radiating 

 oTOOVL'S and .stria' iti the structure of an ordinaiy seale. 

 This marking is most handsome and most regular on 

 the surface of tlie operculum, where it radiates from the 

 articulation (the upjier anterior corner) of the bone, with 

 the grooves, in their even and handsome curves, and the 

 almost smooth ridges terminating at the hind inferior 

 margin thereof. In the f/i/iiuinnis form, where the ossified 

 derma] growtlis are generally more or less reduced, the 

 external bones of the head may also be covered to a great 

 extent by the skin, thus losing their Ganoid appearance. 

 Of the structure of the tins we know alrcadx' how 

 the sjiinous dorsal ra^s var\' in luunber and position. 

 The ordinai'N' jilacc of the first s|)inous ra\' lies at about 

 the end of the lirst third of the length of the body, of 

 the second spinous ra\' at the end of its second fifth, 

 and of the last spinous ray a little behind the middle 

 of tiie body. The most usual supernumerarx' ra\- lies 

 a little in front of the middle of the body. On this 

 head we must remark, however, that in later life the 

 first spinous rav is generally removed distinctly in a 

 forward direi-tion, its average distance from the tip of 

 the snout thus sinking from 32"8 to 30'8 % of the length 

 of the body while this length increases, on an average, 

 from .").V,S to tJIfl mm. The spinous rays are of a, 

 more or less broad, triangular form, with concave or 

 nearly straight sides, and with the front convex and 

 the back concave. The front is rough and lacunose, like 

 the above named parts of the dermoskeleton; the lateral 

 margins are spiniferous for a greater or less distance 

 from the base out towards the subulate tip. The rough- 

 ness and the spines partialh- disappear, however, under 

 the same conditions as the plate-armour of the body, 

 in the qi/nniurKs forms. These spinous rays also vary 

 considerabh- in lengtli. As a rule the second is the 

 longest, tiiough the first may sometimes eipial it in 

 lengtii; the maximum letigth we have found in the latter 

 case, is 42' o % of the distance between the lirst spinous 

 ray and the tip of the snout, while the minimum lengths 

 (in percent of the same distance) have proved to be 

 16 in the case of the first ray, 17 in that of the second. 

 The length of the last spinous ray varies between 7V2 

 and 17 % of the said distance; and this rav generally 



these s])inous I'ays stand straight uji; when depressed, 

 they lie in a straight line with eaidi other, tlu; tip of 

 each ra\' sometimes (when the length of tlie rays is so 

 great) resting on the base of tlie ray behind it. The 

 interspinal plates on wiiich the i-ays are set, are fur- 

 nished with a groove in which tiie latter are ])arth' re- 

 ceived when depressed. Tiiese spinous rays, as well as 

 tiie others (tho.se of tiie anal and ventral fins), are ar- 

 ticulated in such a manner that they can be locked fast 

 by the fish at any angle whatever — though generally 

 and at most in an upright jiosition — and cannot be 

 depressed by force, unless they are simultaneously lifted 

 a little way. This result is attained by the presence 

 at the middle of tiie base of each spinous ray, in ad- 

 dition to its true articulation — a trorldm articulati(jn 

 between each lateral half of the base of the ray and a 

 transverse hollow in the interspinal plate — of a deep 

 fissure (articular cavity), into which is fitted a disk- 

 like, circular process of the interspinal plate. Tlie ])o- 

 sition of the former articulation is a little eccentric 

 i-elatively to this disk, and still more so relatively to 

 the articular pivots of the spinous ray, which bound 

 the said fissure, and which are more elliptical in out- 

 line. Thus, when the spinous i-ay is erected, these 

 pivots with their elliptical friction-siarfaces fall into the 

 circular articular cavity on each .side of the central 

 disk of the interspinal plate. The lower lever of each 

 pivot attains a greater size than the radius of the disk 

 and of the said articular cavities. Any attempt to bend 

 the spinous ray results merely in a pressure partly of 

 the pivots against the walls of the articular cavities, 

 partly of the bottom of the middle fissure of the spi- 

 nous ray against the top of the disk. As soon as the 

 spinous ray is lifted, however, and the said lever thus 

 shortened, the pressure ceases, and the ray falls. Each 

 of the spinous rays has a small, triangular fin-mem- 

 brane behind it. By means of this membrane the last 

 spinous ray is united to the base of the first raj- of the 

 soft-rayed dorsal fin, which in this species begins dis- 

 tinctly in front of the perpendicular from the vent. 

 This fin is of an elongated triangular form, sloping even- 

 ly backwards from the first rays, and finally passing 

 almo.st imperceptibly into the dorsal margin of the pe- 

 duncle of the tail. Its length (base) is about equal to 

 the length of the head in old specimens, in young ones 

 less than the same"; and its height (longest ray) is 



forms a sharp, almost geniculate curve. When erected, 



■■ The specimens we have received from .-Vrcliangel, are marked in this respect, as in several others, by the persistency of the juvenile 



