36 Mr. A. S. Woodward on the 



EXPLANATION OF PLATE IV. 



All the figures, witli the exception of fig-. 4, are from the living subject. 

 Fig. 4 is from a preparation treated with 1 per-cent. acetic acid. Eularge- 

 nient 400 diameters. 



I, First individual (parent animal). 



II. Second individual, produced by division from I. 

 «\ nucleus of the first animal. 



n^, nucleus of the second animal. 

 CV, contractile vacuole. 



Ftff. 1. The plasma begins to withdraw itself from the animal II., pro- 

 duced by division from I. At the bottom of the shell it is still 

 firmly attached and encloses the nucleus w^, which is somewhat 

 elongated. 



Tiff. 2. The process is further advanced, and the plasma is drawn out intn 

 a thin thread. The nucleus ii^ has again assumed its normal 

 form, 



Fiff. 3. The thread is ruptured and the nucleus n^ shows distinct reticular 

 structure ; it is dead. 



Fiff. 4. The expelled nucleus n''' of another animal, after treatment with 

 acetic acid of 1 per cent. 



Fig, 5. The plasma is flowing again into shell II., and emits a pseudo- 

 podium towards the nucleus ?i^. 



Fiff. 6. The pseudopodium has flowed round the nucleus «'■', and is 

 drawing it back towards shell I. 



Fiff. 7. This process has further advanced. 



Fiff, 8. The nucleus nP has lost its structure, and appears as a strongly- 

 refractive irregular mass, 



Fiff. 9. The nucleus m^ is again expelled. 



VII. — Notes on the Determination of the Fossil Teeth of 'KjWo- 

 batis, with a Revision of the English Eocene Species. Bj 

 A. ^MiTH Woodward, F.G.S., F.Z.S., of the British 

 Museum (Natural History). 



, [Plate I.] 



Of all the numerous teeth of Selachian fishes met -with in a 

 fossil state none seem to have been studied with less satis- 

 factory results than those of the well-known genus Myliohatis. 

 Abundantly represented in nearly all the marine Tertiary 

 formations, detached fragments of its dentition have been 

 described under almost endless specific names from various 

 parts of the world ; and the most precise measurements have 

 often been given, without the slightest reference to differences 

 of age or even to variations in the individual jaw. Occasion- 



