COLLECTION OF TUNICIERS. 523 



of the rudistce, which are all fossil, except one 

 lately sent us from the isle of France. 



The 7th and last family, that of the branchio- 

 poda, has hut two genera, the lingula and the 

 terebratula. Only one species of the first is 

 known under the name of duck's bill ; it is a 

 very singular shell, from its two valves being 

 supported on a long peduncle, by means of which 

 it fixes itself upon different bodies. We have 

 seventy- two species of the genus terebratula, 

 sixty of which are fossil; the recent species are 

 sought after by conchologists. 



The following class is the tuniciers, which 

 M. de Lamarck has placed between the*conchi- 

 fera and radiaria, conformably to the recent ob- 

 servations of Savigny, Lesueur and Desmarest. 

 The greater number of its genera are known only 

 by their descriptions, and we possess only about 

 thirty species, which are preserved in bottles 

 next to the naked mollusca. They are marine 

 animals, without heads, and not symmetrical. 

 Some of them are free, others are attached to 

 fuci and various substances. They are divided 

 into two sections, the combined tuniciers or bo- 

 tryllariae, and the free tuniciers or ascidiae. The 

 first order contains those that are agglomme- 

 rated, so that several individuals appear to be 

 animated by a common life, and to form but one 



