MOLLUSCA. 99 



supposes, that they are formed in the interior of an animal 

 analogous to the sepia. The same opinion may, with pro- 

 priety, be entertained of many other genera of multilocular 

 testacea. Faujas St. Fond found a recent specimen of a 

 nummulite among the fragments of the corallina officinalis, 

 brought from the island of Corsica. 



It is probable that the genus LAGENA, formed from the 

 serpulae lagence of Walker's Testacea minuta Rariora, be- 

 longs to the multilocular testacea ; as in some of the species 

 we have observed the appearances of internal, divisions. 



As connected with this division of the Linnsean genera, 

 we may take notice of the British shell called by Lightfoot 

 Nautilus lacustris, (Phil. Trans. Ixxvi. tab. 1). The very 

 circumstance of its being a fresh water shell, distinguishes 

 it sufficiently from all those which we have been consider- 

 ing, and its other characters are likewise peculiar. The 

 partitions are distant, and consist of three testaceous plates, 

 not united, which leave a sufficient opening between them 

 to allow the animal to protrude and withdraw itself. It con- 

 stitutes a distinct genus, which has been termed SEGMEK- 

 TINA, from the trivial name bestowed on it by Solander, 

 which refers to the structure of the septa. Its place in the 

 system is next to the genus planorbis. 



These genera of multilocular shells which we have enu- 

 merated, are those which have been established with the 

 greatest attention. Many other genera might have been 

 enumerated, particularly those formed by Montfort, but the 

 character given of them by Cuvier will satisfy the curiosity 

 of the reader. When speaking of the Conchyliologie $ys- 

 tematique of that author, in reference to this subject, he 

 says, " Ou presque toutes les especes et meme des varietes 

 sont erigees en genres." 



