1908.] ON SHARKS OF THE FAMILY ORECTOLOBID.E. 347 



The following papers were read : — 



1. A Revision o£ the Sharks o£ the Family OrectoloUdce. 

 By C. Tate Regan, M.A., F.Z.S. 



[Received April 1, 1908.J 

 (Plates XI.-XIII .*) 



This revision of the Orectolobiclse was prepared some time ago 

 as part of a descriptive catalogue of the Selachians in the British 

 Museum, a work which I have had no opportunity of continuing 

 for more than two years. I have therefore thought it best to 

 publish some of those parts which are ready. 



The suborder Galeoidei includes Sharks with an anal and two 

 dorsal fins, without fin-spines and with five gill-openings on each 

 side. There are five families, viz. Odontaspididse, LamnidEe,^ 

 Orectolobidse, Scyliorhinidae, and Carchariidfe. The Orectolobidaj 

 are distinguished by the presence of oro- nasal grooves t, by having 

 the last two to four gill-openings above the base of the pectoral, 

 and by the posterior position of the dorsal fins, the first of which 

 is above or behind the pelvics. Anatomically they difler notably 

 from the other Galeoidei in having the mesopterygium expanded 

 distally and bearing nearly as many radials as the metapterygium 

 and in the reduction or absence of the tr-iradiate cartilaginous 

 rostrum. 



In the present revision twenty-one species are recognised and 

 are referred to eight genera ; most of the species are from the 

 Indo-Pacific. 



The considerable range of variation in physiological characters 



* For explanation of the Plates, see p. 364. 



t In most Selachians the nasal cavities are separate from the mouth. In three 

 species of Sci/IiorJiinus {S. canicula, S. edivardsii, and S. marmoratum) the nasal 

 cavities are so near the mouth that the large anterior nasal valves overlie the edge 

 of the upper lip, but there are no oro-nasal grooves. In the Eaiidas oro-nasal grooves 

 are present, but run to the corner of the mouth and do not divide the upper lip. 

 In the Cestraciontidse and Orectolobidge the oro-nasal grooves divide the upper lip 

 into a median and two lateral portions ; they thus correspond in position to the 

 embryonic oro-nasal grooves of the Amniote Vertebrates. 



Most text-books of embryology lay some stress on the presence in Amniote embryos 

 of these grooves, which are supposed to represent an ancestral condition found in 

 the adults of a lower group, the Selachians. There can be little doubt, however, 

 that in the Selachians oro-nasal grooves are specialised structures which have arisen 

 independently in different families, none of which can bo regarded as in any way 

 approximating to the ancestral tj-pe of the higher vertebrates. 



It is now generally accepted that the Amniote Vertebrates are derived from the 

 Batrachians and the latter from the Crossopterygian fishes. In all these groups 

 the prtemaxillary and maxillary bones form the upper border of the mouth and 

 separate the external apertures of the oral and nasal cavities. In the Crossoptery- 

 gians there are no internal nares ; in the Batrachians internal nares are present and 

 develop as perforations of the palate, and in the Amniota they are the persistent 

 inner ends of the embryonic oro-nasal grooves. It seems more likely that in this 

 case ontogeny repeats phylogeny in the Batrachians rather than in the Amniota ; 

 if communication between the oral and nasal cavities internal to the prsmaxillaries 

 and maxillaries originated as open grooves, such grooves must have been present 

 before the development of the prsemaxillaries and maxillaries, but this is improbable, 

 as the Crossopterygians have the bones of the upper jaw fully developed, but no 

 trace of internal nares or oro-nasal grooves. 



