258 



ICHTHYOLOGY. 



C'lassifica- furi-ovved and papillatcil according to the species. The pharyngeal 



tion Ala- hones, large and semicircular, are armed with a pectinated row 



lacopteri. "^ compressed teeth, wliose crowns are wider than their bases ; 

 V 1 and whose size decreases gradually from below upwards. Gill-covers 



^ large. Scales varying in size with the species. The intestine is 



long, and the air-bladder is divided into two in some, into three or 

 even four parts in others, the foremost division having an exterior, 

 thick, iibrous outer coat, which the others want. Twenty-two 

 species. 



Genus XX v. Rhinichthys, Agass. Distinguished from other 

 Catastomi by the conical elongation of the snout. 



Genus XXVI. Sclerognathus, Valenc. Jlouth not quite ter- 

 minal, but the snout advances less beyond it than in the CataUomi. 

 The preraaxUlaries are suspended, as in that genus, under the car- 

 tilaginous extremity of the nasal, have long pedicels, and very short 

 transverse processes, the rest of the orifice being formed by a fibrous 

 ligament within a thin upper lip. The maxillary is a broad solid 

 bone, under which the lip retires, and it is itself hidden by tlie 

 broad preorbitar. Lower lip narrow and thin. The structure of 

 the mouth is that of Catastomus, without the fleshy development of 

 the lips. Mucous pores as in the Catastomi, and also a pectinated row 

 of pharyngeal teeth, but not so large. Air-bladder divided into 

 two, with two small lobules behind the second. Two species. 



Gends XXVII. ExoGLOSSUM, Kafin. Body elongated, little 

 compressed. .Small scales. Anus far baclc. Head without scales, 

 flattened beneath ; mouth terminal ; mandible short, divided into 

 three or five lobes, and resembling a tongue. Ventrals nine-rayed, 

 opposite to the dorsal. Pharyngeal teeth hooked, without denticu- 

 lations, with a small flat crown, and in two rows. No pores on the 

 head. Species five. 



Genus XXVllI. Coditis, ArteJi. Jlouth small, edentate, sur- 

 rounded by from four to eight barbels ; gill-opening a vertical slit, 

 high up; branchiostegals three. Preorbitar hidden entirely by the 

 skin, or in some prolonged into a spine, seldom followed by the 

 other suborbttars, which are absent in most Cohitcs. No solid dorsal 

 ray ; no superior pharyngeals. Scaly fishes like all the Vyprinidae, 

 JI. Agassiz separates the species with spinous preorbitars under 

 the name of Acanthopsis, and ll'Clelland calls the group which have 

 forked caudals Schistura ; but M. Valenciennes does not consider 

 these divisions as natural or established on important peculiarities 

 of structure. Forty-six species are described in the llistoirc des 

 Poissons, in four groups. 



Genus XXIX. B.^litora, Gray. (Platycara, M'Clell. ; Bo- 

 malcptera, Kuhl et Van Ilasselt.) Allied to Cobitis by the edentate 

 mouth, furnished with small barbels, but differing in their flatly de- 

 pressed head, and in the size of the pectorals and ventrals, the bones 

 which sustain these fins forming large plates, from which the fins 

 spread horizontally like those of Callionymus. Body scaly above, 

 naked on the ventral aspect. A short, simple, intestinal canal, with 

 a globular stomach ; no air-bladder. Seven species. 



SILUROIDS. 



This very large family brings up the rear of the Mala- 

 copterygians which have an air-tube to their swim-bladder 

 (Phi/sostomi, Miill.), and in fact some of the rays of their 

 fins are firmer, stouter, and nearly as hard as the spinous 

 rays of the Acantliopleri. It is indeed only when the joints 

 of Malaco])terygian rays have much lengtii tiiat they have 

 great flexibility ; and there are gradations of abbreviation 

 and consolidation until the joints become nearly or wholly 

 obsolete, and the rays as pungent as the first rays of the 

 pectorals and dorsal of the Sihn'oids, which are powerful 

 bony weapons, often strongly toothed or serrated. Yet 

 these strong bones (which, in the fossil state, are named 

 Ichthyodoruhtes) fi-equently betray their compound nature 

 by their tips being soit, flexible, and jointed. 



There are many peculiarities in the skeleton of the Silu- 

 roids, arising trom the absence of some bones, and the greater 

 development of others. The cavity of the cranium is not 

 open laterally, as in most osseous fishes, but is closed, as in 

 the Cypriiiida, by the orbitosphenoids and the ethmoid that 

 unite with the prefrontals, carrying forward the cranial cavity 

 to the nasal bone without leaving a membranous septum 

 between the orbits. The pet)-osal is often wanting in fishes 

 of this family, and some do not possess even the parietal. 

 But the supraocci|)ital is greatly develo|ied, and in many, the 

 suprascapula is miittd by sutiu'e to the sides of the cra- 

 nium. In numerous members of the family the skull is 



enlarged, posteriorly, to form a kind of helmet which spreads Classifiea- 

 oviT the nape ; the lateral angles of this production are tion — Ma- 

 formed by the suprascapula.', augmented and fixed by lacopteri. 

 sutiu'e, and the median part is the extension of the supra- ^"""v^"^ 

 occipital, which stretches out to touch or even articulate 

 with the osseous expansions of the anterior interneurals. 

 The supraoccipital, which is generally very large, articu- 

 lates anteriorly with the frontal, and passing backwards be- 

 tween the postfrontals, the parietals, the mastoids, and the 

 suprascapulae, goes past them all on the nape. The mastoids 

 interpose between the postfrontals and the parietals, so as 

 to come in contact with the supraoccipital, and the parie- 

 tals, but little developed, are pressed to the back part of 

 the cranium, and in some instances wholly disappear. 



The suprascapula most frequently unites to the mastoid 

 by an immoveable suture, which includes the parietal when 

 that bone is present, and extends even to the supraocci- 

 pital ; it gives out besides two processes, one of them resting 

 on the exoccipital and basioccipital, or wedging itself be- 

 tween them, and the other going to the first vertebra; 

 sometimes a plate from the exoccipital su])ports that same 

 vertebra. This vertebra, though it presents a pretty con- 

 tinuous centrum beneath, is in reality composed of three or 

 four coalescent vertebrae, as we ascertain by its diapophyses 

 by the circular elevations of the neural canal and by the 

 holes for the exit of the pairs of spinal nerves. There is 

 great variety in the development of the various processes 

 of the bones we have mentioned, and there is no less in the 

 magnitude and connexions of the first three interneurals. 



In general, in the species which have a strong dorsal 

 spine, the second and third interneiu-als unite to form a 

 single plate, named in the Histoire des Poissons the 

 " buckler," and which is usually more or less crescentic in 

 shape ; the great sjiine is articulated to the third interneural, 

 and there is only the vestige of a spine on the second inter- 

 nciu'al in form of a small oval bone, forked below, ^^hose 

 iunction is to act as a bolt or fulcrum to the great spine 

 when the fish wishes to use it as an offensive weapon. The 

 great spine itself is joined by a ring to a second spine which 

 belongs to the third internem-al. This articulation by ring 

 exists in Lophiiis and a few other fishes not of tliis family. 



The first interneural does not carry a ray, and it varies 

 much in the species whose helmet or casque is continuous 

 with the buckler, as in many of the Bagri and Pimelodes. 

 In these cases the supraoccipital, extending backwards, 

 conceals the first interneural, ])assing over it to touch with 

 its point the buckler formed by the second and third inter- 

 neurals. In other instances, as in Sj/iiodon/is and Aiichen- 

 iplerus, the supraoccijiital and second interneural, forking 

 and expanding, inclose and join themselvest o the first 

 interneural, but leave a larger or smaller space in the 

 middle of the nuchal armour which they contribute to form. 

 When the point of the supraoccipital does not reach quite 

 to the second interneural, the first interneural remains free 

 fiom connection, and occasionally shows us a narrow plate, 

 interposed between the other two ; in such a case the helmet 

 is not continuous w ith the buckler. The neural sjunes of the 

 coalescent centra which form the apparently single first ver- 

 tebra, concur also in sustaining the nuchal plate-armour and 

 the first great dorsal spine ; they carry the interneurals, are 

 joined to them by suture, and one of them is often inclined 

 towards the occiput to assist in sustaining the head ; in fact, 

 this part of the skeleton is constructed to give firm mutual 

 su))port. 



The scapular chain of the Siluroids is also formed to 

 give the resistance to the strong weapon with which it is 

 armed. The suprascapula, as we have said above, is often 

 united by suture to the cranium, and it obtiiins support below 

 by one or two processes that are fixed on the basioccipitals 

 and exoccipitals, and upon the diapophysis of the first verte- 

 bra : no scapula is ever present ; it is between the two arras 



