30 LECTURES ON MOLLUSC A. 



two slender tails at the end of its foot, and a very thin, horny, triangular 

 operculum, very finely serrated on each side. When the operculumis 

 reproduced after injury, very few serrations are formed. In the Plios 

 group, there is only one tail, the eyes are very near the tips of the ten- 

 tacles, and the operculum is claw-shaped, without serrations. The 

 animal and even the operculum is as yet unknown in many of the 

 genera and most of the species of this group : and it is probable that 

 the family will need considerable revision. 



In Buftia, a genus which delights in southern peninsulas, the foot 

 is extremely large, giving a glossy coat to the shell, and the animal is 

 blind. It probably plows the wet sand for bivalves, like Natica. The 

 Pseudostrombs form a transition between these and the ordinary forms, 

 not having any gloss on the spire. The true Nassas are active bur- 

 rowers, curling their nose-pipe up through the twisted notch, while 

 they search the sand for bivalves. They are extremely abundant in 

 tropical seas, both in species and individuals. In Desmoulea the shell 

 is rolled up almost into a ball ; and in Cyclops, it is curiously distorted 

 and flattened like a Nerite. Several of the shells called Nassas, as the 

 common " Buccinum obsoletum" of the west Atlantic, arid Nassa pana- 

 mensis of the east Pacific, have a Pisanoid operculum. I'hey perhaps 

 belong, with Northia,, to the Plios group. The Phos shells are very 

 beautifully cancellated : they have a sharp plait near the breathing 

 notch; and a wave at the base of the outer lip. Nassaria represents 

 the Tritons in this family, and Cyllene the Volutes. 



The Eburnas are very beautifully spotted shells, strong, solid, and 

 more or less shining. They are always smooth, and rarely display any 

 epidermis. They form a transition to the Harps. 



Family PUSIONELUDJE. 



This little group has shells like Fusus, but the operculum is sub- 

 triangular, with the nucleus on the inner margin. 



Family TURRICULIDJE, 



These creatures would be taken forMitras from the shell alone. Indeed 

 the only characters by which the shells can be distinguished are the 

 trifling ones that they are externally ribbed transversely, and the outer 

 lip furrowed within ; characters which in other groups would only 

 amount to specific difference. Here, however, they are coordinate (so 

 far as yet observed) with important characters in the dentition ; the 

 true Mitres being toothed like Fasciolaria, which will be presently 

 described ; while the Turriculw agree with Murex. 



In the remaining family of this group, the foot is greatly developed, 

 causing a more or less glossy secretion over the whole shell. 



Family OLIVID^:. (Olives and Harps.) 



When the foot is very large, we often find the operculum very small 

 or absent. In the Harps and Olives, the foot is deeply chiseled on each 

 side of the front ; so as to make lappels, which may be doubled up over 



