92 LECTURES ON MOLLUSCA. 



and frequently is absent altogether. In the delicacy and transparency 

 of their tissues, they resemble Nudibranchs. 



Family IAXTHINID^E. (Violet Snails.) 



Among the aberrant Heteropods, the lanthinas form an aberrant, 

 not a typical family. The shell is very thin, snail-shaped, with a 

 twisted pillar, angular at the bottom, and a slanting apex. The outer 

 lip is always waved, affording a passage for the exposed gills. All the 

 species are of a beautiful violet color, deepest on the under side, which 

 is more exposed to the light when swimming. The animal has a pro- 

 sobranchiate head, projecting beyond the mantle, ending in a stumpy 

 snout, and armed with two long and two short tentacles. The latter 

 may be regarded as eye-stalks without eyes. As the animals are be- 

 lieved to sleep by day and prey upon the Jelly Fish and Velellas by 

 night, they have no need of them. But the most remarkable appendage 

 is their float, consisting of air-bubbles set in jelly ; which is about three 

 times the length of the shell, and attached to the rudimentary foot. 

 Below this the females fasten their eggs. Buoyed up by these bubbles, 

 the ocean-snails float about in shoals in the open seas of warm climates, 

 and are often cast on shore in vast numbers after storms. The teeth 

 are in numerous series, like Scalaria and Bulla. 



There is only one other genus in the family, Reduzia, in which the 

 violet color disappears, and the shell somewhat resembles Jeffreysia. 



Family MACGILLIVRAYID^. 



The little swimmers which compose this family have not only a 

 normally-shaped shell, but also an operculum. As this is found in 

 addition to the lanthinoid float, it proves that the latter does not take 

 its place in the last family, as had been supposed. The animal has a 

 broad swimming fin, armed with an operculum bearing a support as 

 in Jeffreysia. A breathing-pipe conveys water to the gills, which are 

 covered in. There are two tentacles with eyes at their bases, and tongues 

 armed with teeth and jaw- plates, as in the typical Pectinibranchs. 

 The most remarkable feature however is the crown of four false ten- 

 tacles, branching out behind the head like a collar, as in several of the 

 Nudibranchs, and many times the length of the shell. The pretty 

 little Ethella has the pillar of the shell pointed in front, and the oper- 

 culum on an arm like the Strombs. It appears to be used as a shield ; 

 while the creature skips and jerks with its complex foot. There is a 

 beautiful collar, composed of six elegantly fringed arms. Geindla has 

 a foot like a square-toed shoe, with which it glides along the surface of 

 the ocean. The shell is like a flattened Reduzia, with a few whirled 

 operculum. "This shell-protected speck buoys up its tiny body" in 

 the South Pacific, "cast abroad, though not lost, in the ocean's im- 

 mensity." The singular little shells of Calcarella are abnormally 

 spiral, looking more like those of the Pteropods. They are prettily 

 iringed, like Tricliotropis. The animals have comb-like gills ; long, 

 well-armed tongue-ribbons, and massive, armed jaws. They are crowned 

 with eight fringed arms. All the creatures of this interesting and 



