496 PROCEEDINGS OF THE ACADEMY OF 



Mouth inferior, large or moderate, and more or less arched in front. 



Teeth compressed, and with the edges consequently trenchant or blunt, and 

 entire or serrated ; supplementary prongs are frequently present at their 

 bases. 



Nostrils inferior and lateral near the front margin of the snout. 



Spiracles present and moderately developed. 



Branchial apertures moderately fine on each side, all of which are in front of 

 the pectoral fins. 



Dorsal fins two, each armed in front with a spine, which is more or less ex- 

 posed ; the anterior angle of each fin is more or less rounded, and the posterior 

 acutely produced backwards ; the first is above the space between the pectorals 

 and ventrals ; the second more or less behind the latter. 



Anal tin obsolete. 



Caudal fin obliquely truncated or emarginated, with the upper lobe obtusely 

 angulated at its extremity ; lower lobe obsolete or rudimentary. 



Pectoral fins normally developed, obtusely angulated at the external angle, 

 and rectangular or acutely produced at the interval. 



Ventral fins inserted far behind and nearer the tail than head. 



The family of Spinacoids, as it has been here restricted, is equivalent to 

 the genus Spinax of Cuvier, and embraces only those forms agreeing in physiog- 

 nomy, the shape of the several fins, and the relations of the dorsal spines to 

 their fins. The genus Oxynotus of Rafinesque or Centrina of Cuvier is conse- 

 quently excluded from it. That genus has a very characteristic aspect result- 

 ing from the decided trihedral form of the body and the acute back, the oppo- 

 sition of the second dorsal and ventral fins, and the abrupt attenuation of the 

 tail behind as well as from the shape of the fins, and the insertion of the spines 

 of the dorsal fins. These characters appear to indicate that Oxynotus is less 

 closely related to the Spinacoids than has been generally supposed, and that 

 it is rather the representative of a peculiar family; such being the case, the fam- 

 ily thus recognized should receive the name of Oxynotoidce. The Scymnoids 

 are still less allied to the Spinacoids than the Oxynotoids, as they differ in the 

 form of the head and fins as well as in the total absence of spines from the front 

 margin of the dorsal fins. The Echinorhinoids are still more widely separated 

 by the form of the fins as well as the posterior position of the dorsal and ventral 

 ones. 



The family of Spinacoida? as now restricted appears to be represented at the 

 present day by six genera, which may be briefly distinguished by the characters 

 exhibited in the analytical synopsis herewith given. This arrangement differs 

 considerably from that of Miiller and Henle and their successors. 

 A. Teeth without supplementary lateral cusps. Scales cor- 

 date or rhomboid. 

 ft. Teeth similar in each jaw, with the incisive margin hori- 

 zontal, and terminated at the outer angle in an acute 

 point, directed outwards. 



1. Ventral fins nearly intermediate between two dorsals ; 



pectoral fin obtusely angulated at the inner angle; 



caudal fin with an entire upper lobe Squalus. 



2. Ventral fins little before the second dorsal ; pectoral 



acutely produced at inner angle; caudal with a ter- 

 minal inferior lobe Eutoxyehirus. 



(1. Teeth in upper jaw oblique or vertical. 



1. Teeth in upper jaw vertical and acute, somewhat in- 

 flated on each side of the base; those of lower jaw 

 with the points directed obliquely outwards, ser- 

 rated on the iucisorial or inner margin, and in- 

 flated on the outer side of the base. Scales very 

 small and rhomboid Centrophorus. 



[Oct. 



