158 THE PLAGIOSTOMIA. 



rather large, width less than half the distance from the nostril. Mouth large, 

 width about equal to the distance from the end of the snout, length httle more 

 than half the width; labial folds rudimentary or absent. Teeth similar in the 

 two jaws, oblique with a nearly straight inner margin, and a deeply notched 

 outer, and with very fine serrations in young. Dorsal origin behind the end 

 of the pectoral base, height of fin much greater than length of base; base equal 

 little more than one third of the space between the dorsals, or one fourth of the 

 distance from the snout. Base of second dorsal half as long as that of the anal, 

 origin above the middle of the anal base, end of fin little farther back than in the 

 anal. Caudal nearly one third of the total length; subcaudal lobe much pro- 

 duced. 



Total length 24?, snout to abdominal pores 12, snout to fifth gill opening 

 5i, snout to mouth I5, snout to dorsal Oi, length of caudal 7i inches. 



Specimen described from New York, Prof. Tv. Agassiz. 



Ashy brown; lighter to white below. 



Tropical and temperate Seas. 



CeRTRACION OCEANICA, Sp. UOV. 



Closely allied to C. zygaena, similar in most respects, but distinguished by 

 the following: — body more robust, tail longer, dorsal farther forward, second 

 dorsal ending more directly above the end of the anal, separation between eye 

 and nostril wider, groove from the inner edge of the nostril shorter, concavity 

 above the nostril shallower, mouth smaller, teeth smaller and more oblique, and 

 orbitonarial extension less slender. The origin of the dorsal is above the end of 

 the pectoral base. The teeth are small, the cutting edge of the cusp is so oblique 

 as to be nearly parallel with the base, making the notch on the outer edge very 

 sharp, and giving the sharp angle of the cusp little prominence. In young of 

 C. zygaena, three fourths as long as the types of C. oceanica, the teeth are larger 

 and much more erect. Near the middle of the mouth the cusp in the types is 

 slightly more prominent than farther toward the angles of the mouth along the 

 sides. In the young C. zygaena the notch in the tooth is more nearly a right 

 angle. The length of the oculonarial expansion behind the nostril is greater 

 than its width opposite the mouth clong the hind margin. Compared with 

 C. t tides the hammer is much more oblique, the front margin of the head is 

 much less straight, and the teeth are smaller, more equal and less erect. 



The specimens are grey or ash-colored, yellowish or white beneath, and have 



1 



