ICHTHYOLOGY. 



231 



Selaclii 



Chondrop. flattened process, something in the form of a hoe. The 

 terygn. mouth is small, and below the snout. The second dorsal 

 fin commences over the ventrals, and terminates opposite 

 to the commencement of the low er part of tlie tail. The 

 only known species inhabits the Southern Ocean. See 

 Plate CCCVII. figs. 2 and 3. 



ORDER II.- 



-CHONDROPTERYGII WITH FIXED 

 BRANCH liE. 



Instead of having the gills free at their external edge, in 

 this order we find them fixed all round ; and in respiration 

 water is emitted through as many apertures as there are 

 intervals between the rays. Another peculiarity of this 

 order consists in the small cartilaginovis arches suspended 

 from the soft parts at the outer edge of the branchiBe. 



The Linniean genera Squalusand Baia are the principal 

 members of this order ; but Cuvier and the later Ichthyo- 

 logists have subdivided these into several genera, accord- 

 ing to marked peculiarities in their anatomical structure. 



FAMILY I.— SELACHII, OR PLAGIOSTOMI. 



The palatal and post-mandibular bones support the teeth, 

 while the bones corresponding to the jaws in other fishes 

 are merely rudimentary. A single bone connects these 

 jaws with the cranium, and represents at the same time 

 tympana, jugal, and temporal bones. The os hyoides is at- 

 tached to a single pedicle, and, as in ordinary fishes, sup- 

 ports the rays of the gills. The labyrintli is membranous, 

 and included in the cartilaginous substance of the cranium ; 

 the sac attached to it does not contain, as in fishes, the 

 porcelanous concretions, but masses that are easily pulve- 

 rized. The pancreas has the form of a conglomerate gland. 

 The intestinal canal is short ; but one part of the tube is 

 fvirnished internally with a spiral lamina, that seems intend- 

 ed to prevent the too rapid passage of the food. 



The Selachii have pectoral and ventral fins ; the latter 

 placed behind the abdomen, and on the sides of the anus. 



In some respects their sexual intercourse resembles that 

 of Mammifera. The females have well-developed oviducts, 

 which serve the purpose of a matrix in the species whose 

 young are perfected within the body ; while in others the 

 ova are covered by a tough and horny envelope, to the 

 formation of which a large gland surrounding each oviduct 

 is subservient. These eggs, especially in the Squali, have 

 the form of a parallelogram with long filamentous tendrils 

 at each corner, intended for attaching the egg to Fuci or 

 sub-marine rocks during the maturation of the young in- 

 cluded animals. Many of these eggs are found in a female, 

 but only two appear to be perfected at once. In these the 

 foetus is coiled up, and to its umbilical region is attached 

 a large pyriform bag, of a white colour, by a slender tube. 

 On opening this bag it is found filled with a yellowish, thin 

 liquid, like the yolk of a hen's egg, intended for the nou- 

 rishment of the foetus. When the young animal becomes 

 able to collect its own food, the coriaceous egg opens at 

 one end, the creature escapes, and soon the bag, now 

 empty and useless, drops off. Tlie males are provided 

 with two peculiar organs, placed at the inner edge of the 

 ventral fins. Some have supposed that these are intimately 

 connected with the generative process ; others regard them 

 as mere holders, by means of wiiich the female is more 

 closely embraced by the male. 



Genus Squalus, Linn.; Shark. This forms the first 

 great genus of our present order. The general form is 

 elongated ; the tail is thick, with the spinal cohimn con- 

 tinued into the upper lube ; the pectoral fins are of con- 

 siderable size ; tlie spiracles are on the sidco of the neck ; 



and the eyes on each side of the head. The muzzle is Chondrop- 

 supported by three cartilaginous projections, proceeding teryfjii. 

 from the anterior part of the cranium ; and we can easily Selachii. 

 observe in the skeleton the rudimentary jaws. The sea- """"'V^' 

 pula is suspended in the flesh behind the gills. Some of 

 the sharks are oviparous, while others are viviparous. Dis- 

 tinct but small branchial rays ; there are rudiments of ribs 

 along the spine ; and that column is divided into regular 

 vertebrae. 



The original genus is numerous, and may be divided as 

 follows. 



Genus Scyllium, Cuv. This division is characterised 

 by a short, obtuse muzzle, by nostrils near the mouth, con- 

 tinued in grooves which reach to the edge of the lip, and 

 more or less closed by one or two cuticular lobules. Their 

 teeth have a central point and two lateral prongs. They 

 have spiracles, partly over the pectoral fins. Their dorsal 

 fins are placed iiir back, the anterior not being before the 

 ventrals. All have an anal fin ; and, in some species, its 

 position corresponds to the interval between the two dor- 

 sals ; the tail is elongated, truncated, not forked. 



The most common on our coasts are the following spe- 

 cies. 



Sq. canicula, L. ; greater spotted dog-fish, P. This com- 

 mon and prolific species is very numerous on the northern 

 and western coasts of Britain. The colour of the male is 

 dusky, with numerous distinct small, blackish, spots : the fe- 

 male, of which some naturalists have made another species, 

 is larger than the male, of a more red hue, variegated with 

 deep-brown spots disposed in an ocellated pattern on the 

 sides. The ventral fins of this species have the edge cut 

 obliquely. 



Sq. caivhis, et Sq. stellaris, are also the male and female 

 of another species not uncommon on our coasts. This 

 species differs from the last in size. The spots on its sur- 

 face are fuller and broader ; the ventral fins are more 

 square at the edge. 



To this sub-genuS belong several other Squali, natives 

 of foreign seas. They are distinguished by the position 

 of the anal fin, which is placed behind the second dorsal ; 

 the spiracles are remarkably small ; the fifth branchial 

 aperture is often concealed in the fourth, and the lobes 

 of the nostrils are usually prolonged into cirrhi. 



Among the species are Sq. pendulatus ; Sq. Isabella, 

 Shaw ; Sq. cirr/iatus, Linn. ; Sq. lobatus ; and Sq. tigrinus, 

 Lacep., or Squalus fasciatus of Bloch. 



This last is one of the most beautiful of the order, and 

 has been observed of the length of fourteen or fifteen 

 feet, with a large and blunt head, and tapering body. (See 

 Plate CCCVII. fig. 4.) A kvf years ago one of them was 

 observed for several hours to follow a Liverpool East In- 

 diaman off Madagascar. It was elegantly transversely 

 banded with alternate whitish and dark brown or black- 

 ish fascia; ; and was further variegated by ocellated spots 

 or rings on various parts of its body, which seemed to be 

 about fourteen feet long. Its head appeared to be four 

 and a half feet across ; but the thickest part of its body 

 did not seem more than two feet in diameter. It was 

 accompanied by several pilot-fish, which often swam be- 

 fore, and returned towards it. Several attempts were 

 made to catch it with large baits of fresh meat, but it. 

 never ventured to seize one of them. The lower jaw 

 was distinctly visible whenever it opened its mouth, into 

 which the accompanying fishes seemed to tlie spectators 

 to enter and to leave at pleasure. 



Genus Suualus properly so called, Cuv. This group 

 comprehends all those species with a pointed muzzle, 

 under which the nostrils are placed ; but the latter parts 

 are not terminated by a groove, nor are they furnished 

 with lobules. The tail has more or less of a forked shape. 

 We may farther subdivide this genus in accordance with 



