1906.] SELACniAX FISHES. 741 



Family 1. Chlamydoselaciiid^. 



Body very elongate ; mouth nearly terminal. Pterygo-quadrate 

 not articulated to the cranium. Teeth with broad bases and with 

 three slender erect subconical cusps. 



The only representative of this family is the widely distributed 

 Ghlamydoselachus anguinevs, the anatomy of which has been 

 described by Dr. S. Garman. 



Family 2, Hexanchid^. 



Body moderately elongate ; mouth inferior. Pterygo-quadrate 

 with postoi-bital articulation to the cranium. Teeth with elongate 

 bases and with a series of compressed oVjlique cusps. 



Teeth similar to those of the living Ilexanchus and Ileptranchias 

 are found in Jurassic and Cretaceous strata. The cranium, 

 visceral arches, and paired fins of the two genera of this family 

 have been described by Gegenbaur, the vertebral column by Hasse 

 and Mayer, the median fins by Mivart and Mayer. 



Division 2. G A l e o i d e i. 



Five gill-clefts on each side ; two dorsal fins, neither preceded 

 by a spine ; anal fin present. 



The relationships of the five families which comprise this sub- 

 order may be expressed thus : — 



Scyliorhinidse. Carchariidee. 

 Orectolobidte. | I 



j I 



I Lamnidte. 



Odontaspididifi. 



In the Odontaspididse and Lamnidse the last gill-cleft is in front 

 of or vertically above the origin of the pectoral fin, whilst in the 

 other families it is above the base of that fin. The Carchariidge 

 are remarkaVjle for the development of a nictitating membrane, 

 and the Orectolobidte for the presence of a pair of oro-nasal 

 grooves. 



The pterygo-quadrate is not ar-ticulated to the cranium, which in 

 the typical forms is easily distinguished from that of other Sharks 

 by the structure and ari'angement of the rostral cartilages. These 

 are three rods, of which the lower median one, an anterior pro- 

 longation of the basis cranii, is directed obliquely upwards, whilst 

 the two upper ones, arising from the walls of the olfactoiy capsules, 

 converge inwards, the three nearly or quite meeting anteriorly 

 (text- fig. 118, B, p. 742). This ai^rangement is constant throughout 

 the Odontaspididse, Lamnida?, Scyliorhinidas, and Carchariidfe. In 

 the Orectolobid^e, all of which have a very short and broad snout, 



