PISCES. 241 
the scapular arch complete, and the pectoral fins continuous with the 
head. 
Sub-order 1. Squalide. 
A. Two dorsal fins, one anal. First dorsal above, or posterior to the 
ventral. 
Fam. 1. Scyturmr. 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. Carcuariapini. 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 (P7ri- 
onodon obscurus, United States), Sphyrna. S. zygena is the curious 
hammer-headed shark. Several species of the genus are found fossil in the 
United States. Pl. 84, fig. 1, represents Carcharias verus ; pl. 81, fig. 26, 
Sphyrna malleus, the hammer-headed shark of Europe. 
Fam. 3. Trianopontini. 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.: Tri@enodon. 
b. With both nictitating membrane and spiracles. 
Fam. 4. Gaueini. Spiracles small, longitudinal, orround. 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. Scy.tuiopontini. 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. Musreuini. Spiracles large. Nictitating membrane appearing 
like a duplicature of the lower eyelid. Teeth depressed, without point or 
cutting edge, as in Raiade. First dorsal nearly intermediate between 
pectorals and ventrals. Valve of intestine helicoid. Ex.: Mustelus. 
c. Nictitating membrane wanting, spiracles present. 
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