Vili. PREFACE 
centric, in the direction of layers of growth; radiating, from 
the umbo to the margin. In the spiral univalves ; radiating 
(from the axis of the shell), in the direction of layers of growth; 
spiral, along the whirl, parallel to the suture. In comparing 
the words used to describe sculpture (lire, lirule, strize, striule, 
&c.) with the same words in other books, they should often be 
interpreted as to the appearance of the shell under the micro- 
scope, generally with an inch-achromatic. The vertex applies to 
the whole nuclear portion ; but the apex only to the first whirl. 
Asa slight twist in this may, or may not, be estimated asa 
whole turn, the number of whirls, as stated by different authors 
for the same shell, may sometimes vary.* 
In citing geographical authorities, the name of the first 
observer (not necessarily the collector) is distinguished by 
Italics, in preference to the mark [!| now frequently used; 
since itis not a matter of surprise, but of emphatic fact that 
a certain person brought a shell from a particular place. The 
S. W. Mexican collection, frequently quoted with my initials, 
was brought from a port on “that coast,” probably Acapulco : 
vide Brit. Assoc. Rep. 1857, pp. 281-3. 
The terms expressing frequency are to be understood as 
applying to the collection when I first saw it, after several of 
the shells had been withdrawn by purchasers. They are to be 
interpreted relatively to the total number, and are generally 
used as follows : extremely rare, under a score ; very rare, under 
100 ; rare, under 200; not common, or not uncommon, 300; com- 
mon, up to 400 or 500; abundant, about 600 or 700; extremely 
common, up to 1,000; extremely abundant, more than 1,000. 
The errors which arise from ignorance, those with better 
judgment and means of information will be able to correct. 
The errors of observation can easily be detected, as the shells 
themselves are open to all who desire to study them. It is 
hoped that all such errors will as speedily as possible be detect- 
ed and exposed ; and that this work may soon be laid aside as 
useless, having served its purpose as a stepping-stone to some- 
thing far better. The sooner our own work perishes, the truer 
will be our knowledge of Him whose exquisite order and beauty 
can be abundantly traced, even (asin the following pages) in 
the worm-eaten passages of a decaying shell. 
PHILIP P. CARPENTER. 
Warrington: April 22nd, 1857. 
* This may account for discrepancies in Vitrinella, and in the descriptions 
of the nuclear vertex in Pyramidellide, In this catalogue the number is over 
rather than under-rated. 
