204 GENESIS OF THE ARIETID^. 



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 pilae 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 pila3, 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 saddjes, 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 pihe are 

 developed much more quickly than in this malformed variety ; (3) a variety in 

 which the development of pilas, channels, and keel is still more accelerated, and 

 combined with more gibbous sides and more prominent pike in adults; (4) a 

 variety in which development of the pilge 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 Besancon are dwarfs, having resem- 

 blances to Turneri, Ziet. 



