18. In fine weather they seek their food at liberty, and if a storm arises, the carcinia hide themselves under a stone, and the neritæ attach themselves to it like the patella, the hæmorrhois, and all that class, for they become attached to the rock, where they close their operculum, for this resembles a lid; for that part which is in both sides in the bivalves is joined to one side in the turbinated shells: the interior is fleshy, and in this the mouth is placed. 19. The nature of the hæmorrhois, the purpura, and all such animals is the same. But those which have the left foot greater are not found in the shells of the strombus, but in the neritæ. There are some cochli which contain an animal like the small astacus, which is found in rivers; but they differ from them in having the inner part of the shell soft. Their form may be seen by examining dissections. CHAPTER V. 1. The echini contain no flesh, but this part is peculiar, for they are all of them void of flesh, and are filled with a black substance. There are many kinds of echinus, one of which is eatable; in this one the ova are large and eatable, both in the greater and the less. 2. And there are two other kinds, the spatangus and that called bryttus; these are inhabitants of the sea, and rare. Those which are called echinometræ[133] are the largest of all. Besides this, there is another small species, which has long and sharp spines; this is procured from the sea, in many fathoms water, and some persons use it for stranguary. [133] Echinus esculentus. 3. Around Torona there are white marine echini, which have shells, and prickles, and ova, and are longer than others; but the prickle is neither large nor strong, but soft, and the black parts from the mouth are more in number, and united to the outward passage, but distinct among themselves, and by these the animal is as it were divided. The eatable kinds are particularly and especially active, and it is a sign of them; for they have always something adhering to their spines. 4. They all contain ova, but in some they are very small, and not eatable: that which is called the head and mouth in the echinus is downwards, and the anus placed upwards. The same thing occurs in the turbinated shells, and the patella; for their food is placed below them, so that the mouth is towards the food, and the anus at or on the upper part of the shell. 5. The echinus has five hollow internal teeth, in the midst of these a portion of flesh like a tongue; next to this is the œsophagus; then the stomach, in five divisions, full of fæculent matter: all its cavities unite in one, near the anus, where the shell is perforated. Beneath the stomach, in another membrane, are the ova, the same number in all, they are five in number, and uneven.