SUMMAKY PLATE XIV. (continued). 



Am. Bodleyi, Fig. 27, shows a slightly degenerate compressed whorl, and is the terminal 

 form of the subseries containing IJartmanni. 



Arn. kridioides. Fig. 28 gives a view of the transition between Arnioceras and the lowest 

 species of Coroniceras. The smooth young straight pilse and divergent sides of the adult whorl 

 are clearly shown. The artist has exchanged Fig. S with Fig. 28. 



Cor. Sauzearmm. Fig. 29 shows the later nealogic and ephebolic stages, having the 

 peculiar divergent sides, flattened abdomen, and prominent tubercles of a typical coroniceran 

 form. The young, however, still retain the smooth aspect, indicating derivation from Arnioceras. 



Cor. rotiforme. Fig. 30 represents a form similar to Cor. coronaries. 



Cor. Lyra, Fig. 31. This is as a rule much smaller than rotiforme. The sides are more 

 convergent, and the whorls more compressed and less numerous than in that species. 



Cor. trigonatum, Fig. 32, exhibits the effects of the premature development of old age 

 characters. Fig. 1 on the extreme right shows the dwarfed form of Psil. planorbe, var. lew, 

 from which both the arnioceran as well as the agassiceran series may have been derived in 

 Central Europe. 



Agas. laevigatum. Fig. 33 shows the more compressed variety of this species. 



Agas. striaries, Fig. 34. The striatums were too fine to be represented. 



Ast. obtusum. Fig. 2 shows the stouter variety with well marked channels with stout 

 gibbous whorls and broad abdomen. This has young almost identical with the adults of the stout 

 varieties of Agas. Imvigatum. 



Ast. Turneri. Fig. 36 shows typical variety, with flattened sides and deep channels. It is 

 notably more involute than obtusum. 



Ast. Brooki. Fig. 37 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. 38 gives a view of this remarkable dwarfed form, in which degenera- 

 tion of the pilse and the channels and convergence of the sides have produced morphological 

 equivalence with Oxyn. oxynotum and Guibali. The amount of the involution is greater than in 

 any preceding species of the same series. 



Agas. Scipionianum. Fig. 39 shows the stouter, heavily tuberculated variety, which has 

 young almost identical with the stouter varieties of Agas. striaries. 



Agas. Scipionis. Fig. 40 shows an aged specimen in the Museum of Comparative 

 Zoology, with extremely involute whorls, but keel still prominent. The degeneration of the 

 adult as regards the pilse and form can, however, be inferred from this figure. . The old of 

 Scipioniamcni at the same age is much less changed, and does not exhibit increased involution 

 of the whorls. 



Oxyn. oxynotum, Fig. 41, 42. 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. 

 laivigatum. 



Oxyn. Simpsoni. Fig. 43 shows the stouter form and slightly greater involution of the 

 whorls in this species when compared with oxynotum. 



Oxyn. Lymense. Fig. 44 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. 45 shows the stout form of the whorls better defined, and pilse 

 of this subseries as compared with the oxynotum subseries. 



Oxyn. Lotharingum. Fig. 46 shows the smaller size of this species, and the degeneration 

 of the pilae. The involution of the whorls is, however, greater than in any preceding species. 1 



Oxyn. Oppeli. Fig. 47 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. 



1 The extreme old age of this form is marked by decrease in the amount of involution of the whorl, and also by 

 the loss of the prominent hollow keel. 



