LECTURES ON MOLLUSCA. 41 



those of Bulla and lanthina. There are no central hooks. The lateral 

 teeth are very numerous and regular, arranged in lines forming an 

 obtuse angle. 



The Scalarias are rare, inhabiting deep waters. They are, however, 

 found in all parts of the world, even in the boreal seas. The species 

 are generally very much like one another, and white. The Spaniards 

 at St. Bias wear them as ear-rings, calling them Caracoles finos. The 

 shells with irregular varices are called Cirsotrema. Sometimes they 

 are almost evanescent ; in which case the shell can hardly be distin- 

 guished from Adis. Fossil forms, which may or may not belong to 

 this group, are found as early as the oolitic rocks ; but true Scalarias 

 do not appear till the later cretaceous periods. 



The remaining families of this tribe differ from all the previous 

 ones, and indeed from all other known Grasteropods, in having no 

 teeth on the lingual ribbon. In fact the existence of a tongue at all 

 has to be confirmed. They have, however, a retractile proboscis, and 

 probably live by suction. It is said by some careful observers that 

 the Cancellarias belong to this section. 



Family EULIMID^I, dc. 



The feet in this family are very short behind, but enormously pro- 

 duced in front; and are used not merely for crawling, but for explor- 

 ing in advance. The tentacles are slender, with small eyes immersed 

 in their base. Eulima has a pointed shell, with flat, glossy whirls, 

 and is generally white. The mouth is like Mdania, with a very thin 

 spiral operculum. Leiostraca is very slender and elongated, with 

 periodic thickenings every half whirl. Niso is umbilicated, and often 

 highly painted. Many of the Eulimce, have the axis twisted, especially 

 near the apex. This is very much the case in the group Stylifer, the 

 animals of which live as parasites immersed in star-fish, or on the 

 spines of sea-urchins. They do not appear to have an operculum. 

 The Entoconclia has been found living in Synapta digitaia. 



Family PYRAMIDELLIM. 



These creatures differ from the Eulimas in having the tentacles 

 short, broad, and folded together. The foot is not prolonged in front. 

 The operculum has few whirls, and is very thin, generally wrinkled. 

 There is a rudimentary breathing fold in the mantle. All the animals 

 of this family are born with a reversed spire ; but no sooner do they 

 commence their independent life than they twist themselves round, 

 and continue their growth in the usual right-handed manner. The 

 reversed nuclear shell is generally found at the tip of the apex, more 

 or less immersed in the first regular whirl,, and giving the spire a 

 somewhat truncated appearance: in some species it even projects be- 

 yond the sides of the spire. In the typical group, PyramiaeUa, the 

 shell is sculptured with transverse ribs, and the pillar is armed with 

 strong plaits. The mouth is pinched up in the region of the rudi- 

 mentary breathing hole. The operculum is narrow and notched, to 

 suit the long contracted aperture. In Obeliscus, the shell is smooth 



