130 HTDROZOA. 



SECTION V. 



RELATIONS OF HYDROZOA TO TIME. 



Well-preserved remains of extinct Hydrozoa 

 are wanting. Obscure indications of fossil Sertu- 

 laridce and, perhaps, also of Lucernaridce, have 

 on a few occasions been met with, but of too 

 fragmentary a character to permit of definition. 

 Professor Agassiz, indeed, states that, many years 

 ago his " attention was attracted by two slabs of 

 limestone slate from Solenhofen, the counterparts 

 of one another, upon which a perfect impression 

 of a Discophorous Acaleph was distinctly visible." 



The G-raptolites and ()ldhamiae have, by some 

 naturalists, been referred to the present group. 

 Both, however, may, with more propriety, find a 

 place in the Molluscan class of Polyzoa, 



