Two of these fishes are very common in our markets, one being the Thornback Skate (_Raia clavata_), distinguished by the clawlike spines down the middle of the back as well as on other parts of the body; and the Common Skate (_R. vulgaris_), a very voracious species, from two to four feet long, with a very sharp muzzle. All the members of this family are bottom fish, without air-bladders; and their eggs, which are large and detached, are enclosed in horn capsules which are so commonly washed up on the beach that they are well known to frequenters of the sea-side, who call them Skates’ Barrows or Shepherds’ Purses. These cases are oblong in form, with a process at each corner, and the material of which they are composed looks very much like that of some of the coarser sea weeds after they have been dried in the sun. As a rule only the empty cases are cast ashore by the waves, open at the end where the little skate made its escape; but occasionally we meet with the complete egg, and the case, while still wet, is sometimes sufficiently transparent to show the form of the embryo within. [Illustration: FIG. 230.--THE EGG-CASE OF DOGFISH] Dogfishes are also fairly well known to sea-side ramblers, for not only are some species used as food in many places, but they are also frequently to be seen cast aside with the refuse from the fishermen’s nets. The common Spiny Dogfish (_Acanthias vulgaris_), belonging to the family _Spinacidæ_, frequents all parts of our coasts. It reaches a length of three or four feet, and is of a slate-blue colour above and very pale yellow below. The pectoral fins are very large, the ventral fin absent, and there is a very sharp spine in front of each dorsal. The creature is ovo-viviparous; that is, the eggs are hatched while still within the body of the parent. Another family (_Scylliidæ_) contains two British species without spines, and is also characterised by having the first dorsal fin far behind. They are the Larger Spotted Dogfish (_Scyllium canicula_) also known as the Nurse Dog and the Bull Huss; and the Lesser Spotted Dogfish (_S. catulus_), called also the Huss and the Rough Hound. The egg capsules of both these are occasionally washed on the beach, and those of the latter species may be known by the yellowish colour and the long tendrils by which they are anchored to sea weeds.