ISO WORMS. 



25. Nais. Body creeping, long, linear, depressed, pellu- 

 cid : feet with small bristles each side : feelers none : 



eyes 2 or none. flP 



26. Lernaea. Body oblong, roundish, naked, with 2 or 



3 round tentacula or arms each side by which it 



attaches itself: ovaries 2, projecting like tails from 



the lower extremity. 

 21l Sepia. Body fleshy, receiving the breast in a sheath, 



with a tubular aperture at its base ; arms 8, beset 



with numerous warts or suckers, and in most species 



2 peduncled feelers : head short: eyes large: mouth 



resembling a parrot's beak. 

 28. Triton. Body oblong: mouth with an involute spiral 



proboscis : arms 6 each side, divided nearly to the 



base, the hind-ones cheliferous. 



26. Medusa. Body gelatinous smooth, orbicular, gene- 

 rally flat or concave underneath : mouth underneath, 

 central. 



50. Asterias. Body depressed, covered with a coriaceous 

 muricate crust, grooved underneath, furnished with 

 feelers : mouth underneath, central, 5-valved. 



51. Echinus. Body more or less orbicular, covered with 

 a bony sutured crust, and generally clothed with 

 moveable spines : mouth underneath, 5-valved. 



ORDER III. TESTACEA. SHELLS. 



The calcarious covering of Molusca. 

 A. With more than two valves. 



32. Chiton. Inhabitant of the sheila Doris: shell con- 

 sisting of several plates or valves disposed transversely 

 down the back, and incumbent on each other at their 

 anterior edge . 



33. Balanus. Inhabitant a Triton : shell affixed by the 

 base, of many erect unequal valves. 



34. Lepas. Inhabitant a Triton : shell affixed by a fleshy 

 peduncle, of several unequal valves connected by a 

 cartilage. • 



35. Pholas. Inhabitant an Ascidia : shell with 2 large 

 valves open at each end, and smaller accessory-ones 

 at or near the hinge. 



B. With 2 valves. 



36. My A. Inhabitant an Ascidia : shell generally gaping 

 an one end : hinge mostly with a strong thick broad 

 tooth not inserted into a groove in the opposite valve. 



37. Solen. Inhabitant an Ascidia : shell oblong, open at 

 both ends : hinge with a reflected subulate tooth, often 

 double, not inserted into a groove in the opposite 

 valve. 



