Order XL PLAGIOSTOMI. 



Family Cestracionidte. 



384. The skull of the Port-Jackson Shark (Cestracion Philippi}. 



The scapular arch being detached from the occiput and displaced backwards in Plagiosto- 

 mous fishes, is not here preserved. The turbinal capsules of the organs of smell are well 

 shown ; as likewise the characteristic concavity in the basioccipital. 



Presented by George Bennett, Esq., F.L.S 



385. The tessellated dental covering of the lower jaw of the Port-Jackson Shark (Ces- 



tracion Philippi). Hunterian. 



386. The first, second, and part of the third cervical vertebrae of the Port-Jackson 



Shark (Cestracion Philippi). 



The anterior surface of the atlas presents a deep conical cavity, which is applied to a simi- 

 lar cavity in the basioccipital of the skull. The vertical transverse section of the body of the 

 third vertebra shows a series of nine bony plates, radiating from the centre to the circum- 

 ference, disposed in the long axis of the vertebra, and giving off short processes as they 

 diverge. 



Presented by George Bennett, Esq., F.L.S. 



387. The maxillary and mandibular arches of the Port-Jackson Shark (Cestracion 



Philippi). 



The teeth are arranged, as in the Plagiostomes generally, in several antero-posterior rows, 

 along the margin and inner surface of both jaws ; but the rows are more oblique than in the 

 Sharks, although less so than in certain Rays (Rhino) . The teeth at the anterior part of the 

 jaws are the smallest ; they present a transverse, subcompressed, conical figure, with the apex 

 produced into a sharp point ; these points are worn away from the used teeth at the anterior 

 and outer parts of the jaw, but are strongly marked in those which still lie below the margin. 

 There are six subvertical rows of these small cuspidate teeth on each side of the jaw, together 

 with a median row close to the symphysial line ; and from twelve to fourteen teeth in a row. 

 Behind the cuspidate teeth, the five consecutive rows of teeth progressively increase in all 

 their dimensions, but principally in their antero-posterior extent ; the sharp point is con- 

 verted into a longitudinal ridge, traversing a convex crushing surface ; and the ridge itself 

 disappears in the largest teeth. As the teeth increase in size they diminish in number in 

 each row ; the series of the largest teeth includes from six to seven in the upper, and from 

 seven to eight in the lower jaw. Behind this row the teeth, although preserving their form 



