26 CONTRIBUTIONS TO NORTH AMERICAN ICHTHYOLOGY IV. 



beneath ; liead 4.\ in lengtli, (> to tip of candal; width of head slightly 

 less than length of head. L. 3 to (J feet or more. Atlantic Ocean; 

 abnndant southward; ranginji;- to China. 



{Sqtialits lihuro L. Syst. Xatunc : Zi/ijcviia iihuro Giiiitlier, viii, ;{82.) 



23.— SPHYRI¥A Rafincsque, 1810. 

 Ham ni er-Ji cad A' h arka. 



(Ceatracioii (Kleiu) Gill; Ztjijwna Cuvier; preoccupied.) 

 (R:xiinos(iue, Carattcri di Alcuui Niiovi Generi, etc. : type Squalus zygana L.) 



Head truly "hammer "-shaped, the anterior, lateral, and posterior mar- 

 gins distinct; nostrils near the eyes, the openings confluent with a 

 groove, which extends along most of the front margin of the head. 

 Species few, reaching a large size; found in all warm seas. {(r<fbi)a^ a 

 hammer.) 



32. S. zyjjaena (L.) M. & H. — Uammcr-headed Shark. 



Width of head about twice its length; tirst dorsal large; second quite 

 small, smaller than anal ; pectorals rather largx^ ; color gray. A large 

 shark, found in all warm seas ; common on our coast from Cape Cod 

 southward. 



{Squahis zygania L. Syst. Naturae: Zi/gania ma Urn s Giuithev, viii, 381: Zygcena mal- 

 leiis Storer, Fisli Mass. 238. ) 



Super-family LAMNOIDEA. 



{The Lamnoid Sharl-)^.) 

 Family IX.— ALOPIID^. 



{The Thresher Sharl-fi.) 



Body moderately elongate ; the snout rather short; mouth crescent- 

 shaped ; teeth equal in both .jaws, moderate sized, tlat, triangular, not 

 serrated; the third tooth of the upper jaw on each side much smaller 

 than the others ; gill-openings moderate, the last one above the root 

 of iThe pectorals; no nictitating membrane; spiracles just behind eye, 

 minute or absent; first dorsal large, midway between, pectorals and 

 ventrals; second dorsal and anal very small; caudal fin exceedingly 

 long, about as long as the rest of the body, a pit at its root, a notch on 

 the upper lobe near its tip ; lower lobe moderately developed ; no caudal 

 keel ; ventrals rather large ; pectorals very large, falcate. A single 

 species, reaching a large size, inhabiting most seas ; known at once by 

 the great length v>{ the caudal lin. {Lamnidce, part, Giinther, viii, p. 393 ; 

 genus Alopecias.) 



