of Cartilaginous Fisltes. 35 



Ginglymostoma, Nob. 

 Has small spiracles, the two last branchial openings approximating to each 

 other. The first dorsal fin above the abdominal ones ; the second dorsal fin 

 opposite to the anal. In adult specimens, the inferior part of the fold bor- 

 dering the corners of the mouth, is distinctly separated from the skin of the 

 lower jaw, by a perpendicular furrow. (1 sp.) 



Stegostoma, Nob. 

 The first dorsal fin begins a little before the abdominal ones, standing, 

 for the greater part, opposite to this. The branchial openings are as in 

 Chiloscyllium. A large and thick wreath or rim conceals the upper jaw and 

 the opening of the mouth, which is placed transversely : the nasal valves are 

 reduced to lateral edges of this wreath. (1 sp. Squalus fasciatus, Bl. Schn. 

 3 var.) 



All the Scyllia have the teeth small, pointed, with one or 

 two, or more, lateral denticles en each side. In Stegostoma 

 they are like trifid leaves ; in Ginglymostoma the number of 

 the lateral denticles increases to four on each side. To this 

 group belong, as it seems, all the oviparous Sharks. All of 

 them, whose anatomy we are acquainted with, have the valve 

 of the intestine in the form of a spiral. 



The Sharks of the second division possess, like the Scyllia, 

 an anal and two dorsal fins, and five branchial openings ; but 

 their first dorsal fin is always placed between the pectoral 

 and abdominal fins. They may be divided in the following 

 manner. 



A large group is distinguished by a membrana nictitans, 

 by the situation of the second dorsal fin, which is opposite to 

 the anal one, and by the situation of the branchial openings, 

 the last, or two last of them being always placed above the 

 base of the pectoral fins. We distribute them in two divi- 

 sions, characterized by the presence or absence of spiracles ; 

 and we make subdivisions according to the form of the teeth. 



A. Without spiracles. 



a Teeth flat, sharp, the edges serrated or smooth 



1 . Carcharias. Their flat and sharp teeth are serrated on each side, ei- 



ther in the upper jaw only, or in both. Spiracles are never met 

 with in the adult specimens, though the rudiments of these organs 

 may be observed in the foetus of a few species. (20 sp.) 



2. Scoliodon,N6b. differs only by the teeth being of the same shape in 



the upper and lower jaw ; viz. the points directed towards the cor- 

 ner of the mouth, with a smooth edge, and a truncated protuber- 

 ance, either smooth or indented, on the exterior side of the base. — 

 (5 sp.) 



3. Zygcena; the generic characters of which we need not repeat. Teeth 



as in Scoliodon, but in the adult specimens distinctly serrated. — 

 (3sp.) 



These three genera have the valve of the intestine longitu- 

 dinal and rolled ; an incision near the extremity of the elon- 

 gated upper lobe of the caudal fin, and a small dimple at the 



d 2 



