Till. PEEFACE 



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, paralle 1 to the suture. In comparing 

 the words used to describe sculpture dirse, lirulse, striae, striulse, 

 &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. 

 As a slight twist in this may, or may not, be estimated as a 

 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 it is 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 the shells had been withdrawn by purchasers.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 (as in the following pages) in 

 the worm-eaten passages of a decaying shell. 



PHILIP P. CAKPEOTEE. 

 Warrington : April 22nd, 1857. 



This may account for discrepancies in Vitrinella, and in the description* 

 of the nuclear vertex in Pyramidellid, In this catalogue the number is o.ver 

 rather than under-rated. 



