IV 



mine and the work's best thanks are due for the unlimited 

 confidence with which they entrusted out of their own pos- 

 session their several rarities, and which, I am happy to say, 

 met in no instance with any casualty. To Mr. Curtis I am 

 also indebted for my own means of examining and for Mr. 

 Spry's liberty of delineating at his residence a form extant 

 in no other British Collection ; and likewise to the Officers 

 of the Zoological Department of the British Museum for the 

 urbanity with which they met and forwarded my objects in 

 the several instances I had occasion to examine their rich 

 stores. Having thus paid the debt of gratitude due for 

 being enabled to complete within the short period of twelve 

 months so extensive an undertaking, for which the praise 

 must be bestowed upon the incessant and unflinching per- 

 severance of Mr. Spry, it is next requisite to give some 

 account of my own peculiar portion of the task, as editor. 

 The primary object was to produce a work that should be 

 cheap as well as useful, and to compass the former it was 

 not possible to introduce dissections of the parts of the 

 mouth, which I freely admit are in many instances requisite 

 to show the distinctive differences of certain genera where 

 forms are closely allied, or where in long genera the species 

 range divergently from the types. This would of course 

 have incurred a great cost of time, the value of which must 

 necessarily have been thrown upon the work, and which 

 thus, although it would have acquired to a certain extent a 

 greater degree of utility, would from the additional expense 

 have limited considerably its circulation, for the Enomolo- 

 gists to whom a work of forms is most acceptable and use- 

 ful are the young. A reciprocating task is therefore left to 

 be performed between description and figure : to fulfil the 

 former several English works already exist, and it would 

 have intrenched considerably upon the property of those 



