8 



PI. I. fig. I L, represents a smaller, probably anterior, tooth, with one fang supporting 

 a crown or portion of crown, showing its extreme shortness, increased seemingly by 

 attrition, which has reduced the intervals of the coronal tubercles to low notches of the 

 enamel, with intervening exposed dentine. 



PI. I, fig. 12, shows a minute tooth with a crown of more simple character than the 

 larger molars; it, nevertheless, repeats the characteristic shortness or lowncss of the 

 crown, but shows a more simple tubercular accentuation of the grinding surface, and an 

 indication of two fangs of unequal size; this indication may, however, be due to a basal 

 fracture of a large single fang, as in fig. 11. 



Species 3. — Microlestes rHjEticus, Plate I, figs. 16, 16 a. 



Hypsipryjinopsis rh.eticus, Boyd Daivlnns, 1864.' 



In 1804 Mr. Boyd Dawkins, F.R.S., F.G.S., discovered a small two-fanged, laterally 

 worn molar in Rhaitic marlstone at Watchet, Somersetshire, and, assuming a common or 

 persistent level of the detached patches or ' pockets ' of bone-bed in that county, claims 

 for the marlstone a higher antiquity than the matrix of " the Microlestian teeth of Frome 

 and Dicgerloch.'' 2 



This tooth is figured of the natural size and magnified four diameters,in PL I, figs. 16, 16a. 



The crown, as in Microlestes, is very short in proportion to its fore-and-aft width, 

 being 1 line ( l - 1 2 th in.) in height at the bifurcation of the two fangs, and 2 lines (l-6th 

 in.) from the front to the hind border. The total length of the tooth, including the 

 entire fang, very slightly exceeds the fore-and-aft diameter of the crown. The breadth or 

 transverse diameter of the tooth, cannot be accurately determined, for the side imbedded 

 is " entirely concealed," 3 and the side exposed to view has been subject to attrition, presenting 

 " a smooth polished surface, which extends without interruption from the crown into the 

 fangs," 3 and exposing " a dark band, from b to b, crossing what would be called the base 

 of the crown." 3 This part of the base shows " four grooves passing downwards from the 

 crown towards the fangs.'' 3 Whether these grooves (fig. 16, c) are due to the wearing 

 force or indicate original structure is uncertain ; if the latter, they are repeated in the 

 lower molars of Microlestes and in one of the molars of Flagiaulax, but not in the tren- 

 chant premolars of either this genus or of Ili/psijjrymnus. 



The higher side of the tooth {a b, fig. 16 a) is the one imbedded in the matrix ; so 

 much of it as is exposed shows the upper and inner, not the outer, side ; it is the thick 

 enamelled border of a low crown bounding the inner side of a pounding surface which 



1 " On the Ithsetic Beds and White Lias of Western and Central Somersetshire," &c, 1 Quarterly Journal 

 of the London Geological Society,' vol. xx, 1864. p. 396, &c. 



2 Op. cit., p. 410. 



3 Letter to the Author from Prof. Phillips, F.R.S., dated Oxford, 29th August, 18/0. 



