420 



J. W. DAVIS OIST THE FISH-REMAINS OF 



Pal^osatjrits ? Stricklandi, Davis. (Plate XXII. fig. 6.) 



In the museum of the Geological Society, London, there is a tooth 

 which I "believe to be unique. It is from the Rhsetic bone-bed of 

 Combe-Hill, near Cheltenham, and was presented to the Society 

 many years ago by Mr. H. E. Strickland. 



The base of the tooth is wanting ; the portion remaining is slightly 

 more than -6 of an inch in length. In section (fig. 6 b) the 

 front portion is seen to be more compressed than the back. The 

 lateral extremities of the tooth are slightly produced, and end in a 

 serrated margin ascending to the crown or apex of the tooth, which 

 is smooth. The width nearest the part of the base preserved is '35 

 inch. The surface of the tooth, except along the lateral margin, is 

 covered with fine longitudinal striations, which finally disappear 

 before reaching the point. 



This tooth has the appearance of having been washed and water- 

 worn. The broken portion is smooth and polished; and it is probable 

 that it may have been derived from an older rock, and redeposited 

 amongst the remains of the Fishes and Saurians of the RhEetic age. 



At a meeting of this Society held December 15th, 1841*, a paper 

 was read by Mr. H. E. Strickland on the Bristol bone-bed, in which, 

 along with other fossil remains, he mentions a "portion of a tooth 

 with two finely serrated edges, and considered as probably belonging 

 to a Saurian allied to the genus Palceosaurus there can be little 

 doubt this is the same specimen. I have taken the liberty of asso- 

 ciating the tooth with his name. 



Spheistonchus (Hybodus) obtustjs, Davis. (Plate XXII. fig. 7.) 



The genus Sphenonchus was originated by M. Agassiz for the de- 

 signation of certain objects which are regarded as teeth. It appears 

 probable, as I shall attempt to show, that these oojects were not 

 teeth, but dermal defences. The specimen I am about to describe is 

 •45 inch in length and '35 broad at the base: it is perfect, with 

 the exception of a small fragment which is broken from the right 

 portion of the base. The object, which appears homogeneous in 

 structure, contracts rapidly from the base for a distance of about half 

 its length. At this point its diameter is little more than a third 

 that of the basal portion ; and it remains the same to within a little 

 of the point, which is slightly wider and thinner than the stem. 

 The general form is that characteristic of the genus. It is arched 

 forward, and does not possess any secondary denticles. The upper 

 portion is nearly cylindrical, with the point flattened out like a 

 chisel ; near the base the form is three-sided ; right and left it is 

 produced so as to form wing-like processes ; whilst down the centre 

 of the anterior curved portion a third process is developed, which is 

 continued and increases in size to the lowest portion of the base. 

 The posterior surface, in its basal portion, is slightly hollowed in- 

 wards (fig. 7 h), compensating a little for the ridge in front. The 

 whole of the surface is smooth and covered with shining enamel. 



* Proc. Geol. Soc. vol. iii. pt. ii. p. 585. 



