ON JANASSA BITUMINOSA. 839 



tooth ; rf, second oblique ditto ; e, secondaiy or Petalodontoid 

 form ; /, root of ditto. 



Fig. 2. Primary tooth of J. linguteformis, smooth variety, slightly en- 

 larged : a, scoop-like cutting-margin ; 6, grinding or crushing- 

 sm'face. 



Fig. 3. Primary tooth of the same a little enlarged ; worn variety, inter- 

 mediate between the smooth variety and those much nndidated. 



Fig. 4. Diagram of profile of primary tooth : a, scoop-like cutting-mar- 

 gin ; 6, crushing or grinding-surface ; c, root. 



XVIII. — On Jmmssa hituminosa, Schlotlieim, //'o/h the Marl-Slate 

 of Midderidge, Durham. By Albany Hancock, F.L.S., and 

 Richard Howse. (Plates X, XI.) 



Through the obliging kindness of Joseph Duff, Esq., who has 

 been for many years actively investigating the fossil flora and 

 fauna of the south of Durham, we have lately had an opportu- 

 nity of thoroughly examining the structure of the jaw-teeth and 

 shagreen skin of this most interesting addition to the fauna of 

 the English Marl- Slate, which is the exact equivalent of the 

 German Kupferschiefer. 



Four groups of these remarkable jaw-teeth have been obtained 

 by Mr. Duff at Midderidge — the first group in the year 1865, and 

 the others during the autumn of the present year, 1869. These 

 are, we believe, the first and only specimens that have been dis- 

 covered in England. 



But in Germany this species has been frequently found in the 

 Kupferschiefer, which is very much worked, on account of the 

 valuable copper-pyrites which it contains, in numerous localities ; 

 and consequently the general appearance of these teeth must be 

 well known to those who are familiar with the works of Schlo- 

 theim, Miinster, Geinitz, and others. According to the last- 

 named author, the beautiful specimen still preserved in the Dres- 

 den Museum was well figured in the Dresden Magazine in the 

 year 1762. Afterwards, in the year 1820, it was described by 

 Schlotheim as a Trilobite, under the name Trilohitcs hituminosus 



