1890.] Geology and Paleontology. | 561 
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. 1. This is as a rule much smaller than rotiforme. The 
sides are more convergent, and the whorl more compressed and less 
numerous than in that species. 
Cor. trigonatum, Fig. 32, exhibits the effects of the premature develop- 
ment of old age characters. Fig. 1 on the extreme right shows the dwarfed 
form of Psi. planorbe, var. leve, from which both the arnioceran as well as 
the agassiceran series may have been derived in Central Euro 
Agas. levigatum. Fig. 33 shows the more compressed variety of this 
species. 
Agas. striaries, Fig. 34. The striations 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 Rate almost 
identical with the adults of the stout varieties of Agas. 4 
st. turnert. Fig. 36 shows typical variety, with eke: nee and deep 
channels. It is notable more involute than od¢usu 
st. brooki. Fig. 37 shows an extreme RIA aiy of this species, 
with very convergent sides and narrow abdomen. The channels are almost 
obliterated, and the keel very prominent. 
st. collenoti. Fig. 38 gives a view of this remarkable dwarfed form, in 
which degeneration of the pila and the channels and convergence of the 
sides have produced morphological equivalence with Oxyz. oxynotum and 
bali. 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 extreme 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, Figs. 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. levigatum 
Oxyn. simpsoni. Fig. 43 shows the stouter itn and slightly greater in- 
volution of the whorls in this species when compared with oxynotum. 
Oxyn lymense. Fig. 44 shows the greater involution of whorls as com- 
pared with any preceding form of the same subseries, and the very acute 
degenerate whorl. 
