170 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



being for the most part imperfect, it is a matter of great difficulty 

 and uncertainty to decide to which genus many of them belong. 

 The proposed arrangement of species must, therefore, be considered 

 as a mere approximation, or rather, perhaps, as provisional, until 

 more perfect specimens, or one more skilled in Fossil Ichthyology, 

 shall clear up the obscurity. Several smooth teeth in the Indian 

 collections are remarkable for their regular triangular form. They 

 appear to have been destitute of lateral appendages. The base 

 in this species is broad, equalling the total height of the tooth. 

 The cone is flattened on the outer surface, and rounded on the 

 inner. The enamel of the latter descends lower on the base at the 

 sides than at the centre : the line of boundary thus represents an 

 ascending obtuse angle. The teeth are more or less oblique ac- 

 cording to the position they hold on the jaw. It is one of the 

 smallest species of the genus. 



Lamna complanata Eg. — The occurrence of a small lateral cusp 

 in some of the specimens of this species marks it 

 as belonging to the genus Lamna, although in 

 other respects it would more properly be con- 

 sidered as an Oxyrhina. Its nearest analogies 

 are with Oxyrhina xiphodon and hastalis. It 

 differs from the former in having the outer sur- 

 face more prominent, and the inner one more 

 evenly rounded without the flattened character of the basal portion 

 of the enamel. From the latter it differs in the less prominent 

 contour of the inner surface. It is distinguished from both by the 

 presence of the lateral cusp, in being, infinitely smaller, and in its 

 slender and elegant proportions. The transverse section shows 

 the antero-posterior diameter to be exceedingly narrow — more so, 

 indeed, than in any other species of the genus. 



Lamna sigmoides — It is difficult in a mere verbal description 

 to make intelligible the minute distinctions which, 

 in considering the characters of the fossil squaloid 

 teeth, are the elements on which the species are 

 eliminated. A single tooth sent home by Mr. Cun- 

 liffe recals at first sight the well-known Lamna 

 acuminata of the British chalk. It approaches also 

 that species in size, being one of the largest of the 

 Indian specimens, which, generally speaking, are 

 of unusually small dimensions. In form it is inter- 

 mediate between L. acuminata and L. cuspidata. 

 It differs, however, from both in the sigmoid flexure of the cutting 

 edge. There are no lateral cusps visible. In front it varies from 

 the form of L. cuspidata in the greater breadth of the apex, and 

 from L. acuminata in the parallelism of the sides in the middle 

 region of the tooth. The outer surface is flattened until near the 

 point, where it is slightly rounded. The inner surface is convex 

 and prominent. Seen in profile, the cutting edge conceals the back 

 of the tooth for two-thirds of its length ; it then verges inwards 

 until near the point where it again tends slightly outwards, The 



