38 



POPULAR CONCHOLOGY. 



wrinkled knob ; the chambered portion is some- 

 what spirally curved, describing a half circle ; 

 the partitions are at regular distances, and have 

 a ventral siphuncle. — 1 species, fossil. 



This remarkable genus is manifestly con- 

 nected, by means of the spirally curved shell 

 and the ventral siphuncle, to the Spirula, but 

 resembles, on the other hand, the Beloptera 

 very strongly. 



i 



Sprrvlirostra 

 licllardii. 



Order II. 



TETRABRANCHIATA. (Owen.) 



The animals of this order have four branchiae (whence the 

 name) ; the eyes are pedunculated, and large ; arms very 

 numerous ; body attached to the shell by muscles ; man- 

 dibles shelly, and like a beak. Shell external, chambered, 

 and pearly, the animal only occupying the last chamber, 

 which is very large ; a siphuncle runs through the cham- 

 bers from the first to the last. This order has but one 

 recent genus, Nautilus ; the rest are only found in the fossil 

 state, and they must have existed in immense numbers in 

 ancient seas, for it is stated that there are as many as 

 1,400 species belonging to this order. 



Family l.—NA TJTILA CEA. 



The shells contained in this family have the siphuncle 

 never entirely dorsal, or only apparently so ; the partitions 

 to the chambers are simple, rarely zigzag, lobed or foliated. 

 They arc all fossil with the exception of the genus Nau- 



