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ON THE AX ATOMY OF MULLERIA DALYI, Smith. 



By Maetin F. Woodward, 



Demonstrator of Zoology, Eoyal College of Science, London. 



Head 15th April, 1898. 



The animals (two in number) upon which these observations are based 

 were discovered by Mr. Hubert Bonner, a relative of Mr. E. L. Layard, 

 C.M.G., and forwarded to Mr. E. A. Smith, who described them under 

 the name of MuUeria Balyi} I have to thank both Mr. Layard 

 and Mr. Smith for giving me the opportunity of examining this 

 interesting Lamellibranch. 



So far as I am aware, the anatomy of the type-species of the genus, 

 viz. M. lohata, is quite unknown, and we are but little better 

 acquainted with regard to that of the allied genus Mtheria. Our 

 knowledge of the latter rests mainly tipon the observations of Rang 

 and Caillaud,^ who described, among the macroscopic characters, the 

 relations of the muscles, the mantle, the gills, and the foot. Deshayes^ 

 also gives a brief account, which is evidently taken from that of 

 Rang & Caillaud. Finally, Mr. Smith has briefly described the 

 more obvious features in the external form of MuUeria Balyi. Some 

 important points, however, still remain for me to describe in its 

 anatomy, notably the minute structure of the gills, upon which the 

 classification of the Lamellibranchs is now generally based. 



The Mantle and Muscular System. — The mantle folds are almost 

 completely separated from one another, being united at two points 

 only, viz., at the posterior attachment of the gills, thus separating 

 an inhalent from an exhalent orifice, and dor sally from the posterior 

 end of the hinge-line for about one-quarter of the distance between 

 this point and the attachment of the gills. The margins of the 

 mantle below the attachment of the gills are beset with small sensory 

 papillse for a space which occupies about one-quarter of the extent o'f 

 the mantle-margin from the attachment of the gills to the anterior 

 hinge-line. In ^theria similar papillse occur all round the margin of 

 the branchial chamber, and the mantle lobes are said to be completely 

 disunited. 



The single adductor muscle (Fig. I, j».«.) of the adult corresponds 

 to the posterior adductor of diinyarians, and is situated Just below and 

 well behind the centre of the animal. In the young individual, 

 according to D'Orbigny, two adductor muscles are present, and the 

 shell is said to be anodontiform. 



When a comparison is made between the single adductor muscle in 

 MuUeria and in Ostrea, it is at once apparent that in the former it is 

 very much smaller when compared to the size of the animal than 

 in the latter, that it does not extend so far ventrally, and that it is 



' Ante, p. 14. 



^ Mem. Mus. Hist. Nat. Paris, ser. iii, torn, iii (1834), p. 143. 



2 Lamarck, Anim. sans Vert., 2nd ed., torn, vi (1836), pp. 591-6. 



