THE 



GEOLOGICAL MAGAZINE. 



No. LIX.— MAY, 1869 



I. Dbsckiption of a great part of a Jaw with the Teeth op 

 Strophudus medius, Ow., from the Oolite of Caen in 

 Normandy. 



By Professor Owen, F.E.S. 



(PLATE VII.) 



I HA YE not hifherto seen any specimen so satisfactorily and finely 

 illustrative of the affinity of Stropliodus to Cestracion as that 

 figured in Plate VII. and which is now in the British Museum. It 

 consists of the major part of the dental covering of a jaw, including 

 the posterior part of the symphysis, and shows that the principal or 

 largest crushing teeth are in two rows, in each ramus, the hinder one 

 the largest, as in Cestracion. These are followed by two rows (at least) 

 of smaller crushing teeth, and are preceded by rows of teeth both smaller 

 and more produced at the middle of their working surface, and in the 

 same degree changing from the crushing molar to the conical prehensile 

 type. This dental coating or armature is imbedded in a block of the 

 fine Oolitic building-stone from Caen, which has taken the place of 

 the dissolved cartilaginous support of the teeth, so as to maintain and 

 exhibit the curve of the arch (Fig. la) by which the teeth obliquely 

 overspanned the jaw to which they were originally attached. 



Of the principal row of teeth (a), six are preserved, entire on one 

 side, and the basis of seven on the opposite side of the jaw : the hinder 

 half of this series has been broken off ; the fracture of the supporting 

 matiix there demonstrating the curve of the convexity of the jaw 

 to which they were originally attached. Seven (Fig. la, 1-7) is 

 thus shown to be the normal number of these large crushing teeth, 

 which succeed each other from within, outward, and forward : it is 

 the shell of the innermost and last formed which is wanting on the 

 left side of this jaw. 



The second tooth, counting from behind, on this side (a2), with a 

 grinding surface 0-035 m. m. in length, 0-013 m. m. in breadth, has 

 that surface moderately convex transversely, with the convexity highest 

 toward the fore end, in the longitudinal direction : the outer and 

 inner borders straight and parallel ; the fore and hinder borders 

 curved, but so as to indicate a low angle, fitting the interspace of 

 the correspondingly shaped ends of the two teeth of the contiguous 

 row. The main part of the crown is sculptured by an extremely 

 fine network of thin ganoin, the meshes simulating pores ; but to- 

 ward the hinder slope the threads run together to form fine sub- 



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