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 LacENa, formed from the 
serpule dagene 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 Linnzan genera, 
we may take notice of the British shell called by Lightfoot 
Nautilus lacustris, (Phil. Trans. \xxvi. 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 SEGMEN- 
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 Sys- 
tématique of that author, in reference to this subject, he 
says, “ Ox presque toutes les especes et méme des variétés 
sont erigées en genres.” 
