THE BONE-BED AT ATJST, NEAR BRISTOL. 



425 



than *2 inch in diameter, and it ends in a rounded apex ; rising 

 from the body of the tooth, it first curves a little outward and 

 backward, and then again bends forward, the end projecting, as 

 shown in fig. 10 a, PI. XXII. It appears to be thin in proportion to 

 its width, and has quite a tongue-shaped appearance. The surface 

 of the part of the tooth forming the cone is deeply indented with 

 numerous pituoles. The tip is smooth and is covered with a thick 

 coating of ganoine. The basal line of the lower portion of the tooth 

 is curved inwards from each lateral extremity ; and from the cone 

 the tooth swells with a well-rounded forward curve to the base. 

 Near each lateral extremity of the base a part has been broken away 

 with the matrix. The portion left exhibits the base of a secondary 

 denticle or cone, in the centre of which is the cavity which as- 

 cended towards its point. The secondary denticles were placed 

 forward in comparison with the principal centre one, and were 

 rounder in section. 



This specimen more resembles Agassiz's species G. marginatum 

 than any other ; it may be easily distinguished, however, by the 

 absence of the deeply striated surface which characterizes the 

 latter and by its shorter base. I suggest the nomen triviale C. 

 curtus. 



EXPLANATION OF PLATE XXII. figs. 1-9. 



Fig. 1. Hybodus austiensis, Davis. 



2. Hybodus punctatus, Davis. 



2 a. Transverse section. 



3. Nemacanthus monilifer, var. a. 



3 a. Transverse section. 



4. Nemacanthus monilifer, var. (3. 



4 a. Transverse section. 



5. Nemacanthus minor, Davis. 



5 a. Portion of spine, magnified. 

 5b. Transverse section. 



6. Palceosaurus Stricklandi, Davis. 



6 a. Tooth, magnified. 



6 b. Transverse section, nat. size. 



7. Sphenonchus obtusus, Davis. 



7 a. Ditto, magnified. 



7 b. Antero-lateral form. 

 1c. Posterior view. 



7 d. Postero-lateral form. 



8. Ctenoptychius Ordii, Davis 



8 a. Longitudinal section. 



9. Cladodus curtus, Davis. 



9 a. Longitudinal section. 



Discussion. 



Prof. Seelet remarked on the curious survival in the Aust deposit 

 of Palaeozoic types of fishes mingled with forms peculiar to the 

 Mesozoic as offering a parallel to the mixture of Palaeozoic with 

 Secondary Mollusca in the Upper Trias of the Austrian Alps. He 



