ANATOMY OK PELECYPODA BURNE. 



These facts very dearly point In a somewhat rinse relationship bet ween these three 

 genera, bringing them together ID form a group <>f .Monomyarian An-ida 1 . 



It should lie noticed that in Lissarca the gonads of the two sides are in complete 

 union with one another, as was seen to he the ease in Ail<n'n<ir<-<i by I'elseiieer. hut this 

 is not so in /'/iHiJiri/ii. Here each gonad is separate. 



Another point of interest is the |>resenee of vestigial cephalic eves in Lixxnrai, 

 Adacnarca, Phildbrya, and Barbatia, members of the Aivacca in which these organs 

 have not hitherto lieen noticed. The fact that some of these genera live at a depth 

 as great as 250 fathoms, a region well beyond the limits to which light can penetrate. 

 throws some doubt ou the functional value of these organs. 



Several of the genera described contained eggs either in the mantle-cavity or in the 

 gills (in the anterior part of the mantle-cavity (Adacnarca), in the supra-branchial 

 chamber (Anatina), in the interlaminar space of the gills (Venericardia). I'robahlv 

 in each case the eggs were being incubated; if so, it is a matter worthy of record both 

 because it is an unusual habit among marine Lamellibranchs. and also because it is 

 apparently more common among Antarctic forms than elsewhere. It was found, 

 possibly in adaptation to this habit, that the relations of the gills to the body in 

 Aiititi/Ki < //ij>t/i-i/ were quite unlike those of any other member of this genus about which 

 information could be obtained, but were identical with those that obtain in 3fi/(V/t<nit<i 

 and < 'oi'/ilat/i'xma. 



I cannot close this Report without expressing my thanks to the authorities of 

 the British Museum, in the first place for entrusting me with it, and then for their 

 patience in awaiting its completion. 



V. LIST OF REFERENCES. 



1. DESIIAYES, G. P., 1814-1848. " Histoire Naturelle cles Mollusques '' (Exploration Scientifiijue de 



l'Alg('rie), Paris. 



2. HANCOCK, A., 1853. " On the animal of Myoeliama anoniio'uli'*." Ann. Mag. Xat. Hist. (2), Vol. XI, 



pp. -287-291. 

 ;;. HANCOCK, A., 1853. "On the animal of Chnmontn-a albld,i."Ann. Mag. Xat. Hist, (2), Vol. XI, 



pp. 106-112. 

 4. LACAZE-DuTiiiERS, H. DE, 1883. " Morphologic des Acephales." Icr Mrmoire, " Anatomie de 



1'Arrosoir (Aspergillum dichotomum ''). Arch. Zool. Exper. (-), T. 1. jip. iiO."i -T.'ii', "> pi. 

 o. LovfiN, S., 1849. " Ueber die Entwickelung der Mollusca Acephala.' 1 Arch, fur Xaturgesch., 



Jahrg. 50, Bd. 1, pp. :; 12-339. 

 G. ^MATTHIAS, M., 1914. " Vergleichend-anatomische Untersuchimgen iiber den Darmkanal und das 



Herz einiger Arcaceen." Jena. Zeitschr., Bd. 45, pp. 36341 1, 4 pi. 



7. NOMAX, I), van H., 1881. "Die Lamellibranchiaten, gesammelt wiihrcnd der Kahrtrn di-s ' Willcm 



Barents,' 1878-79." Xirdrrland. Arch, fur Zoo!., Suppl. lid. 1, issl- 1SS2, pp. 1-51, 3 pi. 



8. OniiNER, N., 1912. " Morphologische und phylogenetische Untersuchungen iiKrr die Ncplu-idicn der 



Laiiicllihranchien." Zeitschr. wiss. Zool., Bd. 100, pp. 287-391. 



9. PKLSENEER, P., 1888. "Report on the Anatomy of the Peep-sea Molhisrn, collectcil h\- 11. M.S. 



'Challenger' in the years 187:5-1876 (Pelecypoda)." -" Challenger " Reports, Vol. 27, 

 pp. 31-40, 4 pi. 



