264 SIDNEY F. HARMER. 



III. Description of Eutliyris clathrata, n. sp., of 



E. obtecta, llincks^ and of Euthyroides 

 episcopalis, n. gen. 



IV. The morphology of the compensatiou-sac and of 



the operculum. 



A. Flustrina. 



B. Cribriliuidse. 



c. Lepralioid genera. 



D. Microporelloid genera. 



E. Microporoid genera. 



V. The primary zooscium or ancestrida. 

 VI. Classilicatiou of the Cheilostomata. 

 VII. Summary. 

 VIII. Literature. 



IX. Explanation of Plates. 



I. Methods emi'loyed. 



The choice of species for investigation has been primarily 

 dependent on the material available for the purpose in the 

 collection of the University Museum of Zoology at Cambridge. 

 Spirit material has almost exclusively been used, and I have 

 in the main selected species in which the calcareous matter 

 was not developed to so great an extent as to destroy the 

 transparency of the object. The growing edges of healthy 

 colonies have furnished the most satisfactory results. The 

 material was in almost all cases stained, without decalcifica- 

 tion, in diluted boi'ax carmine for a prolonged period (five to 

 seven days, or even more). After being placed iu absolute 

 alcohol containing picric acid, the fragments were mounted 

 whole in Canada balsam. 



All my more recent preparations have been mounted by a 

 method to which my attention was called by Mr. II. D. 

 Geldart, of Norwich. This consists in transferring the speci- 

 mens diiectly from absolute alcohol to a solution of dried 

 Caiuula b;dsam in absolute alcohol. In preparing this solu- 

 tion, the milky mixture which is at first produced becomes a 



