91 



who are interested in the subject to follow up these observations, and 

 I look forward to some valuable facts being elicited respecting the 

 economy of the genus. 



My endeavours to trace them in Thames mud from other localities 

 much higher up the river, have been entirely without success, but I 

 think this may be attributable to Xanthidium being more a marine, 

 than a fluviatile, genus, which opinion is strengthened by the circum- 

 stance of their being found at New York, in the Mediterranean, and 

 in our own river approximating to the ocean. I shall, however, con- 

 tinue the enquiry, and if anything worthy of note should present itself 

 to my notice, I shall feel great pleasure in submitting it to the 

 Society. 



7, Jeffreys Square, 

 January 14, 1846. 



