The plan is a square surrounded by a colonnade, and the dome seems to be octagonal. Pl. LXXXIV. The square plan below the circular building No. 8, and its elevation to the left, above the plan: here the ground-plan is square, the upper storey octagonal. A further development of this type is shown in two sketches C. A. 3a (not reproduced here), and in Pl. LXXXVI, No. 5 (which possibly belongs to No. 7 on Pl. LXXXIV). Pl, LXXXV, No. 4, and p. 45, Fig. 3, a Greek cross, repeated p. 45, Fig. 3, is another development of the square central plan. The remainder of these studies show two different systems; in the first the dome rises from a square plan,--in the second from an octagonal base._ _Group III. Domes rising from a square base and four pillars. [Footnote 1: The ancient chapel San Satiro, via del Falcone, Milan, is a specimen of this type.]_ a) First type. _A Dome resting on four pillars in the centre of a square edifice, with an apse in the middle, of each of the four sides. We have eleven variations of this type. aa) Pl. LXXXVIII, No. 3. bb) Pl. LXXX, No. 5. cc) Pl. LXXXV, Nos. 2, 3, 5. dd) Pl. LXXXIV, No. 1 and 4 beneath. ee) Pl. LXXXV, Nos. 1, 7, 10, 11._ b) Second type. _This consists in adding aisles to the whole plan of the first type; columns are placed between the apses and the aisles; the plan thus obtained is very nearly identical with that of S. Lorenzo at Milan. Fig. 1 on p. 56. (MS. B, 75a) shows the result of this treatment adapted to a peculiar purpose about which we shall have to say a few words later on. Pl. XCV, No. 1, shows the same plan but with the addition of a short nave. This plan seems to have been suggested by the general arrangement of S. Sepolcro at Milan. MS. B. 57b (see the sketch reproduced on p.51). By adding towers in the four outer angles to the last named plan, we obtain a plan which bears the general features of Bramante's plans for S. Peter's at Rome. [Footnote 2: See_ Les projets primitifs _etc., Pl. 9-12.] (See p. 51 Fig. 1.) Group IV. Domes rising from an octagonal base. This system, developed according to two different schemes, has given rise to two classes with many varieties. In a) On each side of the octagon chapels of equal form are added. In b) The chapels are dissimilar; those which terminate the principal axes being different in form from those which are added on the diagonal sides of the octagon. a. First Class.