1869.] and Membranipora Sengaleiuis. 61 



d. Chemical composition of the polyzoarium. 



When boiled in hydrochloric acid, the polyzoarium left as re- 

 sidue a very thin membranaceous skeleton ; it was complete as 

 regards form of the cells. This membranaceous skeleton could 

 hardly be anything else, than chitin, as distinguished from the 

 common horny substance by being insoluble in hydrochloric acid.* 

 Subsequently I burned several portions of the polyzoria in a platina 

 crucible, until every trace of organic matter disappeared. The cells 

 were by this operation not materially affected, but placed in hydro- 

 chloric acid, they were almost perfectly dissolved, they seem therefore 

 to a very large proportion to consist of carbonate of lime. There was a 

 small residue of siliceous spicule and scleroid particles left, but these 

 were most probably derived from the numerous SponyillcB adhering to 

 the cells. 



e. Habitat. 



Membranipora Bengalensis was found at Port Canning with Sa~ 

 gartia Schilleriana in the same tank of brackish water ; it is, how- 

 ever, much more widely distributed as the last. It also occurs in 

 tanks, the water of which contains only about one fifth of sea-water. 

 I found the species incrusting old trunks of wood on several places 

 along the Mutlah river, on many points in the salt -lakes and in other 

 places of the Sanderban. The present species does not, however, occur 

 in fresh water, where it appears to be replaced by Hislopia, evidently 

 belonging to the same family of Chilostomata. There are a large num- 

 ber of similar forms found on various places of the coast of the Bengal 

 Bay. One of these, with smaller cells, is often seen on shells and 

 fragments of wood coming from the lower portions of the Sanderban, 

 but it is difficult to obtain it in good preservation. 



A marine species which I lately collected at Ceylon and at Aden is 

 very like the one here described but it has the cells much more solid. 



* The plates at the entrance of the cesophngus, or the so-called theeth, 

 have been found also to consist of chitin. 



