PISCES. 241 



the scapular arch complete, and the pectoral fins continuous with the 

 head. 



Sub-order 1. Squalidcs. 



A. Two dorsal fins, one anal. First dorsal above, or posterior to the 

 ventral. 



Fam. 1. ScYLLiNi. With spiracles, and no nictitating membrane; five 

 branchial fissures ; an oral groove ; pectorals broad ; anal anterior, posterior, 

 or inferior to the second dorsal. Caudal elongated, truncate, or rounded at 

 the extremity. No caudal furrow. Teeth with a median cone, and one to 

 four lateral denticles. Colors lively. Ex. : Scyllium, Pristiurus. Recent 

 genera seven. 



B. Two dorsal fins, and one anal. First dorsal between the pectoral and 

 ventral. 



a. Without spiracles, and with a nictitating membrane. 



Fam. 2. Carchariadini. Teeth triangular, flat, with cutting edges, 

 smooth, or denticulated. Anal fin opposite the second dorsal, or nearly so. 

 A small triangular notch generally present, above and below the base of the 

 caudal fin. The nostrils have generally a small triangular valve at the 

 upper border. Convolution of the intestinal valve, longitudinal, not helicoid. 

 Scales small, skin smooth. Ex. : Carcharias, with five sub-genera {Pri- 

 onodon obscurus, United States), Sphyrna. S. zygcena is the curious 

 hammer-headed shark. Several species of the genus are found fossil in the 

 United States. PL 84, jig. 1, represents Carcharias verus ; pi. 81, jig. 26, 

 Sphyrna malleus, the hammer-headed shark of Europe. 



Fam. 3. TRiiENODONTiNi. Valve of the nostrils broad, or even prolonged 

 into a cirrus. Teeth much as in Scyllini. Anal and second dorsal nearly 

 opposite. Caudal notches or furrows, present, or absent. Scales with three 

 to seven ridges. Ex. : Tricsnodon. 



b. With both nictitating membrane and spiracles. 



Fam. 4. Galeini. Spiracles small, longitudinal, or round. Teeth in both 

 jaws equal, flat, with cutting edges ; the jaws oblique externally, anal 

 nearly opposite to the second dorsal. The upper lobe of the caudal fin with 

 one or two notches anterior to the extremity. Convolutions of intestinal 

 valve either longitudinal or helicoid. Scales small, three-ridged, with 

 a central point. Ex. : Galeus. 



Fam. 5. ScYLLioDONTiNi. Snout obtuse. Valve of nostril broad, and 

 tolerably long. Spiracles moderate. Teeth as in Scyllini, one large 

 central fang, with several lateral at the base. Shape of the fins as in 

 this family, the lower lobe abortive, and the caudal furrow wanting. 

 Ex. : Triakis. 



Fam. 6. Mustelini. Spiracles large. Nictitating membrane appearing 

 like a duplicature of the lower eyelid. Teeth depressed, without point or 

 cutting edge, as in Kaiadce. First dorsal , nearly intermediate between 

 pectorals and ventrals. Valve of intestine helicoid. Ex. : Mustelus, 



c. Nictitating membrane wanting, spiracles present. 



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