24 REPORT — 1844. . 



Plate XVIII. — Fig. 40. Tubular structure of Anomia ephippium. Mag- 

 nified 250 diameters (§ 48). — Fig. 41. Decalcified membrane of ditto. 

 Magnified 250 diameters (§ 48). — Fig. 42. External surface of Lima 

 squamosa, showing its cellular structure. Magnified 200 diameters (§ 50). 

 — Fig. 43. Section of internal layer oi Lima squamosa; showing corru- 

 gated structure. Magnified 125 times (§ 50). 



Plate XIX. — Fig. 44. Prismatic cellular structure from Ostrea edulis. Mag- 

 nified 250 diameters (§ 49). — Fig. 45. Ditto from Per7ia ephippium. 

 Magnified 125 diameters (§ 52). — Fig. 46. Ditto from Avicula marga- 

 ritacea. Magnified 125 diameters (§ 52) — Fig. 47. Ditto from iJfa//e2<s 

 albus. Magnified 125 diameters (§ 52). 



Plate XX. — Fig. 48. Ditto from Vulsella. Magnified 250 diameters (§ 52). 



Pig. 49. Ditto from fossil Pinna of Oolite. Magnified 40 diameters 



/§ 52). Fig. 50. Ditto from Gervillia mytiloides. Magnified 125 dia- 

 meters (§ 52). — Fig. 51. Ditto from Unio occidens. Magnified 125 dia- 

 meters (§54). — Fig. 52. Ditto from Etheria. Magnified 125 diameters 



Report on the British Nudibranchiate Mollusca. By Joshua Alder 



and Albany Hancock. 

 The Mollusca Nudibranchiata of Cuvier, although forming a small order in 

 the class Gasteropoda, are sufficiently peculiar in their characters and in- 

 teresting in their zoological relations to allow of their being reported upon 

 separately from the extensive class to which they belong. Their interest in 

 a physiological point of view has also been much increased lately by the re- 

 searches that have been made into their structure and mode of development. 

 The anatomical researches of M. de Quatrefages have disclosed, according to 

 his views, so many peculiarities of conformation in some of the species, that 

 he has been induced to detach a considerable portion of this order, and, uniting 

 them with some other Mollusca rather dissimilar in external appearance, to 

 institute for them a new order, which he has called Plilebenterata. Not en- 

 tirely coinciding with the views which M. de Quatrefages has taken, we shall 

 content ourselves in the present report with considering the Mollusca Nudi- 

 branchiata of Cuvier as still forming one entire group, divisible into two 

 sections, distinguishable from each other by external characters, and probably 

 equally so by physiological peculiarities, the limits of which have not yet 

 been ascertained in the several genera. 



The little animals forming this interesting group were long neglected by 

 naturalists, and were scarcely known to any of our earlier writers. Six spe- 

 cies only were described by Linnaeus in the twelfth edition of his ' S3'^stema 

 Naturee.' These were included in the class Vermes, and formed the genera 

 Doris, Scyllma and Tethys. 'Muller paid more attention to them. Four- 

 teen species are published in his « Zoologia Danica,' the figures and descrip- 

 tions of which, considering the time at which they appeared, are good. Not- 

 withstanding the contributions of Miiller, Fabricius and some others, these 

 animals still continued a neglected tribe, until the appearance of the cele- 

 brated memoirs of Cuvier, published in the 'Annales du Museum,' formed a 

 new era in their history, and laid the foundation of those enlightened views 

 of their structure and affinities which were carried out in his ' Regne Ani- 

 mal,' where the order Nttdibranchiata was first instituted for their reception. 

 It is to be regretted however that so few species were known even in Cuvier's 

 time, and that he was obliged to have recourse to specimens in spirits for his 

 descriptions. So far as their anatomy is concerned the disadvantages arising 

 from this circumstance were not greatly felt, but those only who have seen 



