232 LECTURES ON MOLLUSCA. 



Pterodonia is notched in front, in which respect it resembles the 

 living Ringicula. The shells of this genus are very small, and have 

 been passed on from one place to another, like an English pauper. 

 They have a wry mouth with strong pillar-plates, and a notched lip, 

 somewhat like Halea. They probably form a family by themselves. 

 differing from Tornatella in their glossy texture. 



Family Cylichnid^. 



In this tribe the teeth are arranged in thirteen longitudinal series, 

 greatly resembling Fissurella. The shell somewhat resembles a Torna- 

 tella without plaits, with the spire more or less concealed, and the 

 aperture pinched behind, swelling in front. In some of the forms the 

 apex is prominent and reversed, as in Pyramidellids. The tentacles 

 are united into a broad veil, looking something like a Natica as the 

 creature ploughs through the wet sand. There are however small eyes 

 in front. The deep-water Cylichna has the spire concealed. In the 

 littoral Utricidus it is raised; and in Tornatina there is a columellar 

 fold, and a channeled suture. Certain little shells, closely resembling 

 Radius, have been referred to this family, till more is known concern- 

 ing the animals. Volvula has a posterior canal like the Egg-shells, 

 but a fold on the pillar like Tornatina. Some curious fossil forms ap- 

 pear to belong to this group. 



Family AmphisphyridtE. 



In this little group the shell closely resembles Utricidus; but it is 

 transparent, the eyes being placed behind it, as in Jeffreysia. The 

 tentacles also are like side-fins, and the animal shuts itself up entirely 

 in its shell. The teeth closely resemble Tornatella, but with a square 

 key-stone between the rows of sickles. 



Family Aplustrid.e. 



The shells of this family are generally very highly colored, and are 

 partially covered by the expanded foot-lobes. The animals, also, are 

 highly tinted, and adorned with flap-like tentacles, with eyes at their 

 bases. The tongue-teeth resemble Tornatella; so does the pretty little 

 shell of Bullinula, which has a twisted, but not plaited pillar, notched 

 at the bottom. Ajplustrum, which abounds in the Sandwich Islands, 

 also has a twisted and notched pillar,- with a membranous outerlip ami 

 flattened spire. In Hydatina, the pillar is simple. 



Family Bullid.e. {Bubble-shells.) 



The shells of this family resemble an Ovulum without canals, and 

 with sharp lip. The apex of the spire is generally perforated, and the 

 shell adorned with cloudy painting. The teeth are in arrow-headed 

 rows of sickles, with a hooked key-stone. The Bidlas love slimy 

 places, where they grub for bivalves and other mollusks. The shells 

 of Haminea are thin and horny, almost inclosed by the broad flaps of 

 the foot and head. Acer a has a similar shell, but more flattened, with 



