JO? Mr. fif!C^ on the Genera of Cirnpedes, {Aug, 



Iprab, will most probably form a new genus of this family : it is 

 curious as not being parasitic on vertebrated animals. I have 

 found another exception in A. lavisy living on a specimen of 

 Voiutaporcina, 



The affinity which exists between the families of this group 

 is not very apparent at first sight ; but upon examination, the 

 passage from one to the other is very striking, and sometimes it 

 is very difficult to decide to which family the genera should be 

 referred, as may easily be imagined when I state that both Dr. 

 Leach and Blainville placed the second section of the Anatife^ 

 rid(E as genera of the family PoUicipedidc£y and several of the 

 second section of the latter family are so exceedingly aUied to 

 |he Fi/rgofiiatidfC both in their structure and habits, that 1 was 

 very doubtful to which family they should be referred, nor was 

 I satisfied till I had reason to believe that Lithrotnja, which 

 has many of the characters of Pollicipes, was lithophagous, and, 

 therefore, agreed in habits with Brisnaus and Conchotri/a, the 

 genera under consideration. 



'. Thus the transition of the Pollicipedidcc of the first group to 

 the PyrgoinatidcE of the second, appears very natural, but the 

 genus which forms the junction is yet wanting, for the last 

 genera of the former family may be known from the genera of 

 the Pyrgomatidec by their always appearing to form themselves 

 ^by. chemical action most probably) the holes which they inha- 

 bit, whereas the cells in the corals inhabited by the latter family 

 are caused by the animal raising up its body, and adapting itself 

 to the growth of the zoophyte to which it is attached, which 

 in fact often overruns and destroys it. The passage from 

 the Pi/rgomatida to the Balanidai must be very evident when 

 both Blainville and Mr. Sowerby have placed the genus ^ccrs^o, 

 and Lamarck the genus Coiiopkaj both of which have evidently 

 the habits of the Pyrgomatida as species of the genus Balanys, 



The genus Tetraclita of the second section of the Balanidce 

 wants the shelly base, and has the cellular structure of the valves 

 which is so peculiar a character in the Coronulidcd, which also 

 has only a membranaceous base. 



Another peculiar character of the latter family is that the 

 valves of the operculum are small and distant one from another, 

 ^nd simply imbedded in a membranaceous tunic, which pro- 

 trudes considerably beyond the mouth of the shelly valves : now, 

 as 1 have before observed, as there is reason to believe that 

 the valves of the operculum are analogous to the pdsterior and 

 posterior ventral valves ohheAnatiJhid(c, there must be an evident 

 resemblance in structure between the genera of the 'fiist section 

 of the tatter family, where these vidves are exceedingly small, and 

 the genera of Coro^iulidcc. But this is only an affinit^ of general 

 structure, the genus intermediate between these families is'still 

 a desideratum, for the nearest approximation which I know of 



