1869.] 



EGEKTON GTRODTJS. 



385 



but from this it differs in having the median teeth circular, instead 

 of transversely oval. 



Another specimen belonging to Mr. Mansel is one of great in- 

 terest. There has long been a controversy touching the validity of 

 the genus Sphoerodus. The similarity of the teeth to those of some 

 of the larger species of Lepidotiis induced Agassiz to establish the 

 genus Tvith some hesitation. Owen, however, detected some dif- 

 ferences in the microscopic structure of the tooth, which led him 

 to consider the two genera distinct. Many continental palaeonto- 

 logists, on the other hand, repudiated the genus Sphcerodus, as 

 founded in error. The main obstacle to a satisfactory solution of 

 the difficulty arose from the circumstance that the Bufonites were 

 generally found detached from the dentary bones. In Mr. Mansel's 

 specimen (fig. 5), however, we have true SpJicBrodus teeth, arranged 



Fig. 4. — Vomer of Gyrodus cocco- 

 derma. 



Fig. 5. — Vomer of Sphse- 

 rodus gigas. 



in natural order ; and not only so, but the specimen is fortunately 

 a vomerine bone, the form of which is entirely different from the 

 palatal organization of Lepidotus, and essentially characteristic of 

 the Pycnodonti. The specimen is 2| inches in length, and contains 

 the median series of teeth, the two intermediate rows, and two 

 teeth of the marginal row of the left side. The median row is 

 composed of six teeth of circular form ; the intermediate rows con- 



