LECTURES ON MOLLUSCA. 85 



a slit at the suture, through which a mantle tail runs, as in the Olives. 

 The animal has a very long head, hut no eyes. This is also the case 

 with Atys, the shells of which are strong, white, and generally notched 

 on each side of the lip. 



Family PHILINID^E. (Open Bubble-shells.) 



The shells in this family are never completely rolled-round, but the 

 point of the spire can be seen within. They are situated at the tail 

 end of the animals, which never wholly enter them. The teeth of 

 these creatures consist of two (rarely four) longitudinal series of sharp 

 sickles, turned upwards and often serrated within. Sometimes there 

 are small, buttress-like teeth outside. The animals, like the rest of 

 the Bubble group, have the tentacles merged into the frontal veil, 

 making the head wedge-shaped, for swimming or gliding through soft 

 mud, the resting-place of unsuspecting bivalves. While the blind 

 Naticas deliberately drill their hole and suck out the soft flesh, the 

 dull-eyed Bubbles gobble them down, shells and all, and send them to 

 their gizzard-mill to grind. This consists of three shelly plates, much 

 thicker than the shell-covering of the animal, and working together 

 by means of strong cartilage. An old Italian naturalist called the 

 plates of this gizzard Gioenia, after himself, and described the habits 

 of the invented animal ; so that even Lamarck and Cuvier were de- 

 ceived by it. 



The first group never cover their shells. That of the Scaphander is 

 very large and swollen in front; narrow and projecting beyond the 

 blind animal behind. The green, somewhat pearly shell of the Pacific 

 group Smaragdinella is placed on the middle of the back ; the spire 

 being represented by a cup-like process, as in Calyptrcea. The creature 

 has its tiny eyes in the middle of the veil. Pltanerophthalmus has a 

 horny plate, scarcely bent-in on one side for a spire, at the back of the 

 animal, and partly covered by the foot-lobes. Cryptophthalmus has a 

 similar shell, with the eyes behind the veil. 



In the next group the shell is colorless, and entirely covered by the 

 mantle, at the back of the body. The animals have no eyes. Philine 

 has a very open, slightly-spiral shell, Doridium a flat, triangular 

 plate. Chelidonura has a thin, slightly curved, ax-shaped shell. The 

 animal is very brilliant, with two long tails behind. 



The animals of Gasteropteron and Poster obranchcea require more 

 careful examination. They have no shell, and may belong to another 

 group. 



Family APLYSIADJE. (Sea-hares.) 



In the remaining families of Tectibranchs, the head is drawn out, 

 and the tentacles are distinct. They present the general aspect of Sea- 

 slugs, and, like their land allies, have often a shelly plate to protect 

 the vital organs. The tongue-teeth are arranged in very numerous 

 longitudinal series, in angular cross lines. The sea-hares are grotesque 

 creatures, which crawl about among rock-pools, living on a mixaddiet. 

 They have ear-shaped feelers, with eyes at their bases; a fat body, 

 under the skin of which is an irregular shell, and often rough with 



