400 Mr. W. Clark on Venus undata. 



XXXII. — On the Venus undata of authors. 

 By William Clark, Esq. 



To the Editors of the Annals of Natural History. 



GENTLEMEN, Norfolk Crescent, Bath, March 20, 1852. 



The Venus undata of the older conchological authorities, which 

 has been justly separated from Venus by more recent writers 

 under various appellations, and particularly by the learned 

 authors of the ' British Mollusca ' under the title of Lucinopsis 

 undata, has given rise to much difference of opinion amongst 

 malacologists in regard to its natural position. Though the 

 shell of this species, anomalous in several points, has long been 

 known, the aggregation of the curious chai'acters of its animal 

 has never been sufficiently described, from the difficulty of pro- 

 curing it alive of large size. The quotation from my manuscript 

 in the ' British Mollusca ' is the result of the examination of very 

 small specimens, not more than §ths of an inch diameter, though 

 it is as correct and full as could well be expected from such ma- 

 terials ; but the receipt from Exmouth of adult lively examples of 

 1^ inch diameter, has enabled me to review and add to it several 

 unrecorded features, which I think will interest some of your 

 readers, and show that this peculiar genus has scarcely yet re- 

 ceived its precise natural allocation ; and many important cir- 

 cumstances will be developed, which may assist to determine the 

 proper station of some other bivalve molluscan groups, by the 

 concatenation of characters exhibited by this animal, illustrative 

 of its connection with them. 



Lucinopsis undata, Brit. Moll. 



Venus undata, auctorum. 



Animal inhabiting a shell of thin and fragile texture, like 

 many of the Tellina*, irregularly subrotund, and not exhibiting 

 the decided lenticular form of its shell ; the general colour is 

 pale pinkish drab, which, when the animal has been killed by 

 hot water, often changes to the various hues of orange, red and 

 brown : this remark is of some importance as regards correct de- 

 scription, for under similar circumstances this condition prevails 

 more or less in all the testaceous Mollusca, and particularly in 

 the bivalves. The mantle has its edges sinuated or furbelowed, 

 in some examples irregularly jagged, but not serrated ; the ven- 

 tral aperture is very contracted, only affording space for the 

 issue of a moderately sized foot, in consequence of the basal posi- 

 tion and very large size of the posterior adductor ; and though 

 the anterior one is nearer the dorsal region, it also, from the 

 length, contributes to the smallness of the pedal aperture ; the 



