204 GENESIS OF THE ARIETIDA. 
of the lobes is only two fifths, and that between the cells only one fourth. This 
shows that the proportions in stouter specimens from Boll are not due to the 
greater prominence of the pile and gibbosity of the sides, nor is there any marked 
deviation from the usual rounded outline of either lobes or saddles. A specimen 
of variety D, from Lyme Regis, has sutures with lobes differing one half with 
great uniformity, but saddles differing one half to one third or one fourth, irre- 
spective of this constancy between the lobes. A specimen from Lyme Regis 
shows that there is no correlation between these proportions and the variations 
in outline of the inferior lateral saddles. Thus, in the Lyme Regis specimens, 
No. 1 has the inferior lateral saddles flattened and rounded; No. 2, pyramidal, 
with two marginal saddles forming a club-shaped expansion at the top; No. 4, 
straight sides and slightly concave base ; No. 5, like No. 1 again; and No. 7, like 
No. 4. 
The sutures of the first specimen described from Bempflingen as having the 
microceran pile, have the usual proportions of others. A specimen from Lyme 
Regis has lobes differing from one half to three fifths, the saddles, however, 
with remarkable constancy, remaining about one half, as far as measured. The 
wounded specimen described above had lobes and saddles, varying from one. 
half to the excessive difference of five sevenths, and the extremes of difference 
were not the nearest to the fractured portion of the shell, but some sutures 
removed from the fracture. A small specimen from Whitby, on the third quar- 
ter of the fourth volution, showed lobes differing from one half to three fifths, 
and saddles from nearly equal to one third, A somewhat larger specimen from 
Lyme Regis had lobes differing three fourths, and the saddles three fourths and 
two thirds on the first quarter of the sixth volution. On the right side of a speci- 
men from Lyme Regis a rare distortion occurs. The first auxiliary lobes are 
obsolete, or at any rate only represented by a marginal lobe, and the first and 
second auxiliary saddles form a solid bank. 
By combining all of these observations, it becomes possible to trace a series of 
modifications. There is evidently (1) a very immature form or variety, in which 
a microceran aspect is assumed through pathological causes; (2) a variety in 
which a low keel, very shallow narrow channels, flat sides, and depressed pile are 
developed much more quickly than in this malformed variety ; (3) a variety in 
which the development of pile, channels, and keel is still more accelerated, and 
combined with more gibbous sides and more prominent pile in adults; (4) a 
variety in which development of the pile is accelerated, accompanied by the 
advent of broader and deeper channels, and a more prominent keel in the later 
_ stages. The specimens from Salins and Besangon are dwarfs, having resem- 
blances to Zurneri, Ziet. 
