frum the Marl- Slate of Midde ridge. 57 



jaw, and composes the posterior half of the general batch. 

 These are arranged in tlie same fashion as those of tlie upper 

 jaw ; but instead of having the anterior scoop-Hke cutting- 

 margins turned downwards, tliey arc ])Uiccd in tlie ojjposite 

 direction, looking upwards. The anterior margins of tlie two 

 sets of teeth meet in the transverse middle line, and are pressed 

 close together, so that the entire batch is continuous, there 

 being no hiatus anywhere, the mouth, in fact, being closed, 

 and the teeth of the two jaws pressed together. In the under 

 jaw there are likewise five horizontal rows of seven teeth 

 each, though, on account of the injury the specimen has sus- 

 tained, the exact number is not so easily determined as it is 

 in the other jaw. 



This specimen has apparently been as complete as that 

 figured by Munster (Beitr. Heft v. Taf. 15. figs. 10, 11) under 

 the name oiJ. Dictea^ and is, indeed, a very good counterpart of 

 the specimen there represented,* only in ours the front or scoop- 

 like cutting-margins of the teeth are bmied in the matrix, the 

 view of the specimen being obtained as it were from the oral 

 cavity ; while Count Miinster's figure has the front of the 

 teeth exposed, as they would be seen had the fish been laid 

 upon its back. 



Another of Mr. Duff's specimens (PI. III. fig. 1), however, 

 presents the same aspect as that of the figure just referred to, 

 and is almost perfect, rising as that does in bold relief from 

 the matrix, in the fonn of an irregularly rounded cluster, hav- 

 ing the peculiar vesicular appearance seen in most of Munster's 

 figures. This appearance is very remarkable, and at first 

 sight has, as was suggested to us on showing the specimen to 

 a friend, no little resemblance to a cluster of ova-capsules of 

 Fusus anfi'quus, particularly Avhen the teeth are a little dis- 

 turbed. 



In connexion with this cluster of teeth, a large patch of 

 shagreen is beautifully displayed, and enables us to determine, 

 in like manner as in the former instance, which is the anterior 

 margin of the specimen, the spreading of the shagreen indica- 

 ting the direction of the body of the fish. 



In this specimen, as in the fu'st-mentioned, the teeth are di- 

 visible into two sets, which have their cutting-margins opposed 

 to each other across the transverse median line. Those of the 

 anterior set belong to the upper jaw, and are closely packed to- 

 gether and interlocked in the manner previously described, in 

 four transverse or horizontal rows ; the remains of a fifth row 

 are distinctly visible. The an-angement is the same as in the 

 first-described specimen : that is, in each row there is a cen- 

 tral tooth with three lateral ones on each side, the extreme 



