68 M. G. St-Hilaire on the service which the Trochilos 



equally different from those which are now generally adopted. 

 We find an alternation of strata which, singly observed, would 

 be considered as belonging to the chalk and to the tertiary for- 

 mation. The principal reason which would lead to such a re- 

 sult would be the nature of the fossils observed in these beds ; 

 but since they have formations alternate, they cannot form any 

 sufficient ground for separation, and we may consider them 

 either altogether as being parts of one formation, or make a 

 division, and consider the one as real chalk, the other as be- 

 longing to the tertiary formation. If the latter is the case, and 

 I am of opinion that such a division is fully warranted, the line 

 which separates the two formations can nowhere be drawn, ex- 

 cept where, in the cliffs of Stevensklint, the bed of clay com- 

 mences ; and we consider the upper bed of Stevensklint, the 

 cliffs of Moen, the cliffs of Rugen, notwithstanding their fos- 

 sils, as belonging to the tertiary formation. The reasons which 

 lead me to make the division in the place mentioned, are the 

 different laws of stratification above and below this point, al- 

 though it cannot be denied that the one passes into the other 

 by degrees, — the first appearance of such fossils as are consider- 

 ed belonging to the tertiary formation, — the nature of the rock, 

 which approaches a great way to that of the tertiary formations 

 of other countries. 



Art. VIII. — An account of the services which the little bird 

 called Trochilos renders to the Crocodile. By M. Geof- 

 froy St-Hilaire. 



On the 28th January 1828, M. Geoffroy St-Hilaire commu- 

 nicated to the Academy of Sciences of Paris, a paper upon two 

 species of animals called Trochilos and Bdella by Herodotus. 



The author began by announcing that his memoir was, pro- 

 perly speaking, only a commentary on a short passage from 

 Herodotus. 



" When the crocodile,'" says this great historian, " feeds in 

 the Nile, the inside of his mouth is always covered with bdella 

 (a term which the translators have rendered by that of Leech.) 



" All birds except one fly from the crocodile, but this one 

 bird, the Trochilos, on the contrary, flies towards him with the 



