

PREFACE. 



J.N an early stage of my inquiries into the structure of that interesting 

 class of Animals which forms the subject of the present treatise, I had 

 it in contemplation to limit them to the space of a brief memoir, which 

 I had intended to submit to the Linnean Society ; as, however, these 

 inquiries proceeded, aided by the acquisition of numerous new and 

 important specimens, and by the kind contributions of my scientific 

 friends, they gradually swelled to such a bulk (and more particu- 

 larly the plates requisite for their illustration increased so greatly in 

 number) that I could no longer flatter myself that a Society whose 

 objects are so general, would deem it expedient to sacrifice so large a 

 space in its transactions to a single branch of Natural History, and 

 still less to incur on such an account, so great an expense as regular 

 engravings of such numerous details would necessarily have entailed. 



Under these circumstances, many of the friends to whose inspec- 

 tion I had submitted my collection of these remains, and whose 

 acquaintance with the subject entitled their opinion to an high degree 

 of deference, were kindly anxious that I should still communicate 

 the result of my investigations to the Public, by offering on the terms 

 of Subscription, a Monograph of this Class to which they related, 

 and applying the slender talent of drawing I possessed, to executing 

 myself the necessary illustrations in a series of Lithographical Plates, 

 as the only mode in which a private individual could bring forward 



