QUADRILATERALS. How many sides has the figure _a b d c_? What is it called on account of the number of its sides? Name three other quadrilaterals whose vertices are marked. Name seven by numbers. Quadrilaterals are sometimes named by means of two opposite vertices. The quadrilateral _a b d c_, or _c d b a_, may be read _a d_, or _b c_, or _c b_, or _d a_. Name the quadrilateral, _g h f e_, four ways. How many angles has each figure? On account of the number of their angles they are called _quadrangles_. Has the quadrilateral _a d_ any two sides parallel to each other? Then it is called a _trapezium_. _A trapezium is a quadrilateral that has no two sides parallel._ Name two other trapeziums. Why is Fig. 7 a trapezium? Has the quadrilateral _e h_ any two sides parallel? Which two? Are the other two sides parallel? It is called a “_trapezoid_.” “Oid” means like. What does “trapezoid” mean? _A trapezoid is a quadrilateral that has only one pair of sides parallel._ Name another trapezoid. Why is Fig. 6 a trapezoid? How many pairs of parallel sides has the quadrilateral _i l_? Name the horizontal parallels. Name the oblique parallels. It is called a “_parallelogram_.” _A parallelogram is a quadrilateral whose opposite sides are parallel._ Name five other parallelograms. Why is Fig. 4 a parallelogram? Why is not Fig. 6 a parallelogram? Why is not _e h_ a parallelogram? What two names may you give to Fig. 5? Why is it a quadrilateral? Why a trapezium? What two names may we give to Fig. 6? Why is it a quadrilateral? Why a trapezoid? What two names may we give to Fig. 3? Why is it a parallelogram? Why a quadrilateral? LESSON TWENTY-FIFTH. REVIEW. How many quadrilaterals in the diagram. (DIAGRAM 20.) Why is Fig. _a d_ a quadrilateral? What is a quadrilateral? On account of the number of its angles, what may it be called? Name all the quadrilaterals. Name three trapeziums. Why is Fig. 5 a trapezium? What is a trapezium? Name two trapezoids. Why is Fig. 6 a trapezoid? Name its parallel sides. What is a trapezoid? Name six parallelograms. Why is Fig. 4 a parallelogram? Name its two pairs of parallel sides. What is a parallelogram? What two names can you give to Fig. 4? Why the first? Why the second? What two names may be given to Fig. 7? Why the first? Why the second? What two to Fig. 6? Why the first? Why the second? [Illustration: Diagram 21.] LESSON TWENTY-SIXTH. KINDS OF PARALLELOGRAMS. RHOMBOIDS. How many quadrilaterals in the diagram? (DIAGRAM 21.) How many parallelograms? Has the parallelogram _a d_ any right angle? It is called a “_rhomboid_.”