4 A MONOGRAPH OP THE 



naturalist to adopt the more modern views of the French school. At present it comes behind 

 the knowledge of the day, and is chiefly valuable as a document in the history of the science. 

 The Nudibranchs described in it amount to twelve, of which two or three are varieties, and 

 the rest have now been described by other authors. The first arrangement of the British 

 species into modern genera was given by Dr. Fleming in his ' Philosophy of Zoology,' and 

 subsequently in his 'History of British Animals/ which appeared in 1828. This work 

 contains twenty species of NudibrancJiiata, six of which were introduced into our fauna for the 

 first time ; viz. — Doris Icevis, Boris nigricans, Tritonia Hombergii, Tritonia arbor escens, Eolida 

 plumosa, and Eolida purpurascens. In 1838 Dr. Johnston published his excellent Monograph 

 of the f Scottish Mollusca Nudibranchia' in the first volume of the 'Annals of Natural History.' 

 It comprises an anatomical and physiological account of the animals contained in the order, 

 and goes far to extricate the synonyms from the obscurity in which they had been involved. 

 The species new to Britain introduced by Dr. Johnston, either in this treatise, or previously 

 in Loudon's 'Magazine of Natural History,' amount to eight: they are Boris obvelata 

 {JoJmstoni, A. and H.), Boris pilosa, Tritonia plebeia, Triopa clavic/er, Triopa notkus, Melibcea 

 pinnatifida (fragilis, For.), Eolidia Cuvieri, and Eolidia rufibrancJdalis. From this period much 

 more attention has been paid to the Nudibranchiate Mollusca by British naturalists, and new 

 genera and species have been discovered in increased ratio. This has resulted partly from 

 the more extensive explorations of our coasts by means of the dredge that have been so 

 successfully carried on of late years, but principally from the more careful mode of investigating 

 nature that naturalists now find it necessary to adopt. The researches of Professor Edward 

 Forbes have added considerably to our knowledge of the NudibrancJiiata ; eight or ten new 

 species have been contributed to the British list by his means. To Mr. Thompson, of Belfast, 

 science is also indebted for much information and several new species in this department, 

 obtained during his extensive investigations into the natural history of Ireland, now, 

 unfortunately, put a period to by his untimely death. Shortly after the publication of 

 Dr. Johnston's memoir, the authors of the present work first began to turn their attention to 

 the Nudibranc/iiata. Since that time they have had the good fortune to introduce into our 

 fauna upwards of sixty species, principally the result of their own personal researches ; for 

 the knowledge of a few of them, however, they are indebted to friends, particularly to 

 Mr. W. P. Cocks, of Falmouth, to the Rev. D. Landsborough, jun., of Saltcoats, and toMr. 

 Barlee. The number of British species now described in this work amounts to one 

 hundred.* 



It will not be necessary here to enumerate the additions that have been made to this 

 department of the European fauna during the last half century. Sufiice it to say that of late 

 years much attention has been paid to the NudibrancJiiata by continental naturalists, and 

 several new species have been described. Among the authors treating of the subject may 

 be mentioned, Risso, D'Orbigny, Cantraine, Quatrefages, Sars, Loven, Delle Chiaje, Philippi, 



* The second volume of Sir J. G. Dab/ell's ' Powers of the Creator displayed in the Creation/ 

 published since the above was written, contains descriptions of twenty .five species of Nudibranchiate 

 Mollusca, most of which are familiar to us. Two or three species may possibly be new, but the 

 descriptions are too imperfect to found an opinion upon, especially as they come very near to others 

 already known. Some interesting remarks on the habits and embryology of these animals will be 

 tound in the work. 



