SUMMARY PLATE XIII. 
Agas. levigatum. Fig. 1 shows the more compressed variety of this species. 
Ast. obtusum. Fig. 2 shows the stouter variety with well marked channels (a little too 
deeply shaded), with stout gibbous whorls and broad abdomen. ‘This has young almost identical 
with the adults of the stout varieties of Agas. levigatum. 
Ast. Turneri. Tig. 3 shows typical variety, with flattened sides and deep channels. It is 
notably more involute than obtuswm. 
Ast. Brooki. Fig. 4 shows an extreme involute variety of this species, with very conver- 
gent sides and narrow abdomen. The channels are almost obliterated, and the keel very 
prominent, 
Ast. Collenoti. Fig. 5 gives a view of this remarkable dwarfed form, in which degenera- 
tion of the pil and the channels and convergence of the sides have produced morphological 
equivalence with Oxyn. oxynotum and Guibali. The amount of the involution is, however, 
greater than in any preceding species of the same series. 
Agas. striaries. Fig. 6 gives a view of the adult, with a decided keel. 
Agas. Scipionianum. Fig. 7 shows the stouter, heavily tuberculated variety, which has 
young almost identical with the stouter varieties of Agas. striaries. 
Agas. Scipionis. Fig. 8 shows an aged specimen in the Museum of Comparative 
Zodlogy, with extremely involute whorls, but keel still prominent. The degeneration of the 
adult as regards the pile and form can, however, be inferred from this figure. The old of 
Scipionianum at the same age is much less changed, and does not exhibit increased involution 
of the whorls. 
Oxyn. oxynotum, Fig. 9,10. The first figure shows the young of a variety in which at 
an early stage there is close likeness to the young of Agas. striaries, and the adults of Agas. 
levigatum. 
Oxyn. Simpsoni. Fig. 11 shows the stouter form and slightly greater involution of the 
whorls in this species when compared with omynotum. 
Oxyn. Lymense. Fig. 12 shows the greater involution of whorls as compared with any 
preceding form of the same subseries, and the very acute degenerate whorl. 
Oxyn. Greenoughi. Fig. 13 shows the stout form of the whorls better defined, and pilee 
of this subseries as compared with the oxynotum subseries. 
Oxyn. Guibali. Fig. 14 shows more involute whorls than in Greenoughi. 
Oxyn. Lotharingum. Fig. 15 shows the smaller size of this species, and the degener- 
ation of the pile. The involution of the whorls is, however, greater than in any preceding 
species. 
Oxyn. Oppeli. Fig. 16 shows the extremely involute form of the Middle Lias. The stout 
whorls indicate that no great amount of degeneration had taken place. It may have been a 
direct descendant of Greenoughi. 
