PLAGIOSTOMI. 



131 



Hyhodus longiconus, have been discovered in the old red 

 sandstone in the vicinity of Petersburg. 



In the Orodus, the cones are more compressed, trenchant, 

 and distinct from the body of the 

 tooth, than in Hyhodus; but they 

 present a principal and secondary 

 cones. Fig. 45 is a tooth of the 

 Orodus ductus (Ag.), from the car- 

 boniferous beds near Bristol. The 

 O.porosus and 0. compressus are from 

 deposits of similar age near Armagh. Diplodus and Glossodtis 

 of the coal series, and Sphenonchus, which ranges from lias to 

 wealden, are referred to the Hybodont family. 



Fig. 45. 



Orodus cinctus (tooth). 

 (Carboniferous.) 



Family III. — Squalid^e. 



(Sharks.) 



The well-marked saw-shaped tooth (fig. 46), so closely re- 

 sembles the lower jaw-teeth of the sharks, called "grisets" by 

 the , French (Notidanus, Cuv.), as to be referred to that genus 

 by Agassiz. Such teeth nevertheless occur in strata of oolitic 



Fig. 46. 



Fig. 47. 



Fig. 48. 



Notidanus Miinsteri. 

 (Upper Oolite.) 



Cor ax falcatus. 

 (Chalk.) 



Gcdeocerdo aduncus. 



(Miocene.) 



age (Notidanus Miinsteri, Ag., fig. 46). Other species — e.g., 

 N. pectinatus — are found in the chalk of Kent ; and JS T . serra- 

 tissimus, in the eocene clay at Sheppy. 



The tooth (fig. 47) on which Agassiz has founded the genus 

 Corax, indicates by its close resemblance to those of Ca.reharias, 

 its relationship with the true sharks (Squalidce). Most of the 



