6 



MANUAL OF THE M0LLTJ8CA. 



the Brachiopoda, forai the sub-class of Molluscoida. In the 

 first edition the Tunicata were described in detail, but they are 

 omitted in this for reasons stated in the preface. 



Five of these modifications of the moUuscan type of organi- 

 sation were known to Linnaeus, who referred the animals of all 

 his genera of shell-fish to one or other of them ; * but unfortu- 

 nately he did not himself adopt the truth which he was the 

 first to see ; and here, as in his botany, employed an artificial, 

 in preference to a natural method. 



The systematic arrangement of natural objects ought not, 

 however, to-be guided by convenience, nor " framed merely for 

 tie purposes of easy reniembrance and communication." The 



Fig. 7. A Bivalve. t Fig. 8. A Tunicary.? 



true method must be suggested by the objects themselves, by 

 their qualities and relations ; — it may not be easy to learn, — it 

 may require perpetual modification and adjustment, — but inas- 

 much as it represents the existing state of knowledge it will aid 



* The Linnffian types were— Sepia. Limax, Clio, Anomia, Ascidia. Terebratula 

 was included with Anomia, its organisation being unknown. 



t Mya truncata, L. k. From Forbes and Hanley. 



% Aacidia mentula, Miill. Ideal representation ; from a specimen dredged by Mr. 

 Bowerbank, off Tenby. 



