FIFTH, OR AGASSICERAN BRANCH. 203 
first mode of development for two and a quarter volutions. The increase is 
gradual, so that well defined pile are not produced until the last of the third or 
first quarter of the fourth whorl. An English specimen of variety A has large 
tubercles on the second quarter of the third whorl. These continue at long 
intervals, only about two to a quarter of a whorl. The true pile do not begin 
to appear until the third quarter of the fourth volution. “Even then these are 
exceedingly oblique and fold-like, and, though they soon assume the aspect of 
true pile, retain their obliquity until the second quarter of the fifth volution. 
Another English specimen shows acceleration by developing similar tubercles 
on the last quarter of the second volution, and also by the development of per- 
fect straight pils on the second quarter of the fourth volution. A third speci- 
men of variety E, from Lyme Regis, has tubercles beginning on the last quarter 
of the second whorl, and perfect pile on the last part of the first quarter of the 
fourth volution. 
Var. Smithi. 
The British Museum possesses a card with several young specimens of the 
variety Simiti, which at first appear to be identical with the full grown devgatum 
or striartes. They have short living chambers, becoming more or less contracted 
at, the apertures, and fold-like pilz with striations. They have not, however, the 
peculiar form of the young of /evgatum, Plate VILL Fig. 10, 13, nor similar 
sutural digitations, and the living chamber is about three fourths of a volution in 
length. It’ is interesting to note here the fact, that acceleration in the develop- 
ment of the tubercles and pile occurs in variety E, which has more involute 
shells than other varieties. 
Ast. obtusum has characteristic sutures, and the number of specimens usually 
exhibiting these parts were also favorable for testing the diagnostic value of the 
proportions of the lobes and saddles in the definition of the species. We have 
made large numbers of measurements, of which the following are selections. 
The fractions express the differences between the abdominal and superior lateral 
lobes, or the inferior and superior lateral saddles. The abdominal lobe and infe- 
rior lateral saddles being always longer, the fraction expresses at the same time 
the proportionate lengths in equal divisions of these two. 
A specimen of variety B, from Robin Hood’s Bay, has three sutures on the 
third and two on the fourth quarter of the fifth volution, with a difference of 
only two fifths between lobes and saddles, and one septum on the third quar- 
ter, in which the lobes are equal, the saddles remaining unchanged. One from 
Teuchsloch bei Bempflingen has lobes varying from one fifth to one third, and 
saddles from one sixth to two thirds. A specimen of variety C, from Boll, has 
these proportions in none of its sutures, but either two fifths or one half between 
the lobes, and one fifth or one third between the saddles. Comparisons were 
made upon sutures of the same age in each case. Another specimen of this 
variety from Boll, having similar gibbous sides, has similar proportions between 
the lobes and saddles, with exception of the eighth suture, in which the difference 
