TRAKSACTIOXS OE SECTION D. — UEl'X. ZOOLOGY AND BOTANY. G73 



4. On the Affinities of Proneomenia} By Dr. A. A. W. Hubrecht. 



One of the forms of animal life which have heen looked upon as aberrant by 

 successive investigators of moilusks and collectors of shells is the genus Chiton, 

 with its allies, Chitonellus, Cryptochiton, &c. Instead of a regular bivalve or 

 iinivalve shell these animals carried along the median line of tlieir backs a series 

 of calcareous plates, forming, on closer inspection, so manj- separate shells, the one 

 behind the other. 



By the possession of a radida, they appeared closely allied to tlie other Odon- 

 tophora ; by a certain amount of bilateral symmetry they seemed to resemble the 

 lameUibranchiates. 



Very recently certain points in then- internal organisation, more especially con- 

 cerning the nervous system, gave rise to their being entirely removed (wrongly I 

 think) by a German morphologist from tlie Mollusks and placed in the sub-division 

 of Worms. 



Of late years otlier, yet more perplexing, forms liave come to liglit. One of 

 them, discovered by Professor Loven, of Stockholm, appeared to be a very small- 

 sized worm, and was, up to the last two or three years, arranged with the Gephy- 

 reans, and called Chcetoderma. Its anatomy was first investigated by Professor 

 von Graff, and more completely in 1877 by l)r. Hansen. 



The second genus to which I allude was first described by TuUberg, in 1875, 

 found off the Swedish and Norwegian coast, and lately proved, by the Rev. A. M- 

 Norman, also to inhabit the British coasts. To it the name of Neomenia was 

 assigned. 



Opinions differed as to its ueai'est allies. Some placed it with the worms, 

 others with the mollusks. Von Graff pointed out its close relationship to Chsetoderma, 

 whereas the distinguished British morphologist, Professor Ray Lankester, created 

 a separate phylum for it, which he placed in the immediate vicinity of the Chitons. 



Von Thering was the first to propose that the Chitons, Chretoderma, and 

 Neomenia should all be united in a separate class, which he called the class of the 

 Amphineura. 



The year before last the Dutch expedition which, in the vessel Willcm Bm-^f.s, 

 yearly sets out for explorations of the Arctic seas, brought .with it two specimens 

 of an animal, which not only proved this arrangement to be a very natural one, 

 but also by its minute anatomy actually furnishes several links by which the 

 disconnected genera above mentioned are held together. 



The specimens were placed in my hands, and, in working them out, I was 

 more fortunate than several of my feUow-workers in this one respect, that my 

 results were not forestalled by the publication of an English report on the same 

 subject which appeared last year, and in which some of the most eminent of 

 your specialists described the different marine animals brought home by the Dutch 

 exploring vessel from a collection of specimens which had found theii-'way to the 

 Exeter Museum ! 



The comparative study was unexpectedly facilitated by the kind generosity with 

 which Professor Ray Lankester, who had made an excellent series of sections 

 through the specimens of Neomenia collected by Mr. Norman, put these sections 

 at my disposal, although his intention in preparing them had been to work up 

 the subject himself. 



I may now call your attention to those facts by which either the affinity of 

 the different genera of the Amphineura is demonstrated, or even in some cases 

 light appears to be thrown on the phylogeny of the MoUusca in general. 



The external shape is very simple, in wliich respect it corresponds with Neo- 

 menia and Chsetoderma ; in size, however, it considerably surpas,ses them, measur- 

 ing about 15centim. ; the body is rounded, shows no external appendages whatever, 

 whereas ventrally a very fine groove is perceptible, in front and behind of which 

 the anterior and posterior openings leading into the animal's intestines are situated. 



' Published in the Supplement Band zum Niedei'ldndischen ArcMv.fiir Zooloqie. 

 Leyden. 1881. 



1881. X X 



