ON THE ANATOJiir OF FISHES. 
247 
2. Siluriche Ahnormales. 
Omitting for the present any reference to such extremely aberrant forms as 
Hypophthalmus, Rliinelepis and the various Loricaroid genera, we confine our summary 
of this group to the various genera and species that came directly under our notice. 
These are : — Clarias, Saccobranchus, Eutropiichthys, Cryptopterus (two species), 
Ailia, Schilbichthys, Silondia, Acrochordonichthys, Ahysis, Pimelodus (two species), 
BagariuSy Glyptosternum, Euclypto sternum, CaUomystax, and Cetopsis. 
In all these forms the series of rigidly interconnected vertebrae includes only the 
first, the complex, and the fifth vertebrae, the sixth being almost invariably free. 
The rigid articulation of the anterior vertebrae with the skull is as marked in this 
group as in the preceding one, and is brought about by substantially similar means. 
The centrum of the first vertebra is usually somewhat more rudimentary than in the 
normal forms, and neither it, nor the basioccipital, nor the complex centrum, are ever 
provided with accessory articular processes. Subvertebral processes are never 
developed. The complex vertebra has the same general characters as in the foregoing 
group. The spinous processes of the third and fourth vertebrae form, as a rule, a con- 
tinuous thin lamina of bone, usually articulated along its dorsal edge with the supra- 
occipital spine, and it but rarely happens that the spine of the fourth is cleft for the 
support of the first interspinous bone which, therefore, is usually supported by the 
bifid spine of the fifth vertebra. Superficial bony deposit may thicken the sides of 
the complex and fifth vertebral centra, and even invest the lateral and ventral 
surfaces of the first centrum, or, in addition, extend on to the basioccipital, partially 
or completely obscuring the various intervertebral sutures. A median groove for the 
dorsal aorta is generally indicated, but rarely {e.g., Pimelodus sapo) becomes con- 
verted into a complete canal for any portion of its extent. Asymmetrically developed 
cardinal grooves are almost always present, but in one or two instances {e.g., 
CaUomystax) are absent. Dorsal laminae and radial nodules are usually, but not 
invariably, present ; exceptionally, the dorsal laminae have no connection at their 
inner extremities with the complex centrum {e.g., Clarias, Glyptosternum), and when 
this is the case the radial nodules may be absent {e.g., Glyptosternum), or confluent 
with the inner extremities of the dorsal laminae, and widely separated from the 
complex centrum {e.g., Clarias). 
The most characteristic of the various skeletal modifications exhibited by this group 
is the formation of more or less complete osseous grooves, recesses, or funnels for the 
partial or complete enclosure of the air-bladder. Such recesses are formed by the 
transverse processes of the fourth vertebra, either singly or in conjunction with those 
of the fifth vertebra, and vary greatly in depth, and in the extent to which they 
are surrounded by bone. They may be comparatively shallow and widely open on 
the ventral surface {e.g., Bagarius, Ahysis, Acrochordonichthys, &c.) ; or may take 
the form of deep, transversely dispo.sed grooves, contracted distal ly, but somewhat 
