402 Mr. W. Clark on Venus undata. 



pear in no tribe but in that of the Veneres, give it a decided con- 

 necting link with them. 



As to the alliance of Lucinopsis with Lucina it is not very 

 near, and principally consists in its lenticular shape, which, how- 

 ever, is that of many of the Veneres, so that a less significant 

 appellation might have been preferable. I must likewise observe, 

 that there are some differences of shape and position from either 

 the Tellince or Veneres in the adductor cicatrices of Lucinopsis, 

 which have a slight approach to the Lucince ; in other respects 

 there is little in common between the two, there being no sipho- 

 nal apparatus, and a very peculiar foot in Lucina. 



These remarks may induce malacologists to take into consi- 

 deration that, the Tellinidce and Veneridce being so closely allied 

 by the intervention of Lucinopsis, it would be desirable to re- 

 move the Mactrcs into the vicinity of Cyprina, to follow it and 

 precede Cardium, in which case the line would march thus : — 

 Tellinidce, including the Donaces, Lucinopsis ; the Veneridce, em- 

 bracing Cyprina and its adjuncts ; then Mactra, Cardium, &c, 

 which two latter genera as regards both the animal and shell 

 have some points of agreement, and by relieving the Tellinidce 

 and Veneridce of the intermediacy of the Mactrce, perhaps a 

 greater approach to a natural position would be obtained. 



The peculiar characters of the shell of Mactra create a diffi- 

 culty with respect to natural order, as it has many features of 

 the Myadce and Anatince ; but the open mantle of the animal will 

 not allow it to be so near a neighbour to them as to precede the 

 Tellinidce ; neither can it remain between the latter family and 

 the Veneres, the union of which I think is more naturally effected 

 by Lucinopsis, notwithstanding the anomalies that exist in that 

 genus. The siphons of Mactra are altogether different from those 

 of the Tellince; their tubes are more congruous with the Vene- 

 ridce, so that it might have been placed immediately after the 

 typical Veneres if the Cyprinidce had not intervened, which, how- 

 ever, cannot be severed from them, merely because their siphons 

 are so short as scarcely to produce a scar ; — therefore it would 

 appear difficult to fix Mactra otherwise than to follow the Cypri- 

 nidce, and come into line with the Cardia. 



I am, Gentlemen, your most obedient servant, 



William Clark. 



Erratum in the paper on Lepton Clarkice, ' Annals,' N. S. vol. ix. p. 293 : — 



For " I was all but convinced that the Lepton convexum and L. nitidum 

 were identical," read " I was all but convinced that the Lepton convexum 

 and L. nitidum were distinct." 



