38 Scientfiic Proceedings, Royal Dublin Society. 



position of the nerves, that the first definite gill-cleft in Ammo- 

 coetes is identical with the hyoid cleft in elasmobranchs. 



In conclusion, Dohrn refers to Shipley's recent paper on 

 some points in the development of Petromyzon fluviatilis. 



The description given by this investigator confirms Dohrn's 

 views that the pseudobranchial groove is homologous with the 

 spiracle. The objection raised by the Belgian authors, therefore, 

 falls to the ground, so far as that point is concerned, at any rate. 



