532 A. Smith Woodward — The Cretaceous Saw- Fish. 



tooth is broad and acuminate, compressed antero-posteriorly, and 

 fixed upon a depressed base ; the crown is marked by large vertical 

 wrinkles, and its median portion is more or less produced down- 

 wards anteriorly over the root.' 



Branchial Apparatus. — The branchial arches are only seen im- 

 perfectly from below in one specimen (B.M. No. 49546), and this 

 furnishes the evidence for our restoration. The great broad basi- 

 branchial plate exhibits at its anterior margin evidence of two pairs 

 of forwardly directed processes, a delicate inner pair somewhat 

 convergent in front, and a larger outer pair divergent. The five 

 hjfjiobranchial cartilages on each side are nearly uniform in size ; 

 and the two hindermost pairs are in distinct connection with the 

 body of the basibranchial. 



Axial Skeleton of Trunk. — The vertebrfe are robust and distinctly 

 tectospondylic, the centra being somewhat deeper than long and 

 depressed-oval in transverse section. The constriction of the ver- 

 tebral centra is slight. There are traces of slender ribs (not shown 

 in the figure) in the region of the pelvis, but precise details as to 

 their extent and arrangement cannot be ascertained. 



Api^endicidar Skeleton. — In the paired fins the slender cartilaginous 

 rays extend to the outer margin, are articulated at distant intervals, 

 and bifurcate distally except in the most anterior portion of the 

 pectorals. The shoulder girdle is hypothetically indicated in the 

 figure, its remains in all known specimens being obscui'e ; but the 

 basal cartilages of the pectoral fins are well shown in several cases. 

 The propterygium is considerably extended forwards and supports 

 about 16 rays; the mesopterygium is narrow and bears 8 rays; and 

 the metapterygiuin, much produced backwards, is the largest element 

 supporting not less than 25 rays. The pectoral fins ai'e triangular 

 in shape and relatively large, each much exceeding in bi-eadth the 

 width of the pectoral arch ; and their posterior apex almost reaches 

 the pair of pelvic fins. The pelvic arch is slender, and the basi- 

 pterygium is much elongated, bearing about 22 rays of which the 

 most anterior one is considerably thickened. Of the median fins 

 thei'e are no certain indications, though it seems not unlikely that 

 the little triangular expansion on the left side of the extremity of 

 the tail in the principal specimen of the trunk,^ will prove to be the 

 second dorsal. 



Dermal Structures. — The skin is covered with numerous very 

 small stellate tubercles, some spinous, some indented in the centre, 

 and those on the snout gradually passing into the single paired series 

 of rostral teeth. The lateral borders of the head, the anterior border 

 of the paired fins, and the sides of the tail are also strengthened by 

 much more robust, small, smooth tubercles, closely arranged in a 

 dense cluster. 



Systematic Determination. 



The Selachian thus described is shown by its vertebral axis to 

 belong to the suborder Tectospondyli ; and in the general form of 



1 Catal. Foss. Fishes, B.M., pt. i. pi. ii. fig. 4. 

 - Catal. Foss. Fishes, B.M., pt. i. pi. ii. fig. 1. 



