108 Owen — New Sauroid Fish, 



that member of the Upper Oolite series at Culham, Oxfordshire, and 

 now forms part of the choice collection of William Cunnington, Esq., 

 F.G-.S., of Hillworth, Devizes. 



The most instructive and characteristic specimen consists of the 

 chief part of the dentary element of the left ramus of the lower jaw 

 (Plate V.) It is unusually broad above in proportion to its depth, for 

 the purpose of due provision of space for the attachment of the two 

 ranks of the dental array. The outer and inner sides of the bone 

 meet at almost a right angle (iig. 3), and form a sharp ridge, 

 which there defines the lower contour of the mandible. The outer 

 side of the dentary is slightly convex vertically, 1 inch 2 lines deep, 

 smooth, and with a polish at some well-preserved parts of the 

 surface. The outer margin of the alveolar tract rises where it forms 

 that part of the base of attachment of a tooth, and the surface sinks 

 slightly below this part. The dentary is gently bent to this short 

 symphysis, producing a corresponding degree of convexity of the 

 outer, and of concavity of the inner, surface, leng-thwise. The 

 inner surface inclines at its upper border toward the inner rank of 

 small teeth, which are attached a little way from the convex border so 

 formed, not close to the edge, like those of the outer rank to the outer 

 border. Below the inner border the surface is slightly concave 

 vertically, and deepens to form the angular depression (fig. 2) for 

 the attachment of the splenial part of the angular element of the 

 mandible. 



The number of teeth of the outer rank, indicated by wholes or 

 parts, in place and use, at the same time in the present portion of 

 the dentary, is 9. The first and second have been broken away by 

 recent-looking posthumous fracture from their places of attachment. 

 An empty depression of corresponding size between them, indicates 

 a tooth that has been naturally shed,. — a like depression intervenes 

 between the second and third tooth. This is entire, as is also the 

 fourth in close contiguity therewith. Then follows an interspace 

 of an empty socket, and the succeeding five teeth are separated by 

 such intervals equalling at their bottom the antero-posterior extent 

 of the teeth in place. These are conical, very slightly curved 

 inward and backwariJ^, and sharp pointed : they are seen of the 

 natural size in Plate Y. The transverse exceeds the fore-and-aft 

 diameter of the attached base. The outer side of the base does not 

 show the impression characteristic of such teeth in Thlattodiis. The 

 enamel is laid upon the upper half of the crown ; it is smooth and 

 glistening. The cement slightly thickens where it coats the lower 

 or basal half of the tooth. 



Of the inner rank of mandibular teeth fifteen are presei-ved in 

 the same extent of the alveolar tract as supports the nine outer 

 teeth. These, as is shown in fig. 2, are more recurved and also 

 incurved than the outer rank, and generally, though slighly, de- 

 crease in size as they are placed further back. 



The two ranks of teeth come pretty close together at the sym- 

 physial part of the mandible, but soon diverge, showing the extent 

 of transverse interspace, for example, between the third tooth of 



