Mr. W. Clark on Venus undata. 401 



mantle is produced posteriorly into two very long pale orange 

 siphons divergent and separated to their bases; the branchial 

 one is the smallest and longest, being in adult examples in full 

 extension 1^ inch long, and having the extremity margined by a 

 circle of very short, minute dark lines, blotches or dots, with 

 16-20 white cirrhi of irregular sizes and lengths ; the anal siphon 

 is of rather larger diameter, and when protruded is barely an 

 inch in length ; its extremity is furnished with 12-15 white, 

 short cirrhi, of more uniform length than in the branchial ; it 

 has not the dark terminal margin of points : the usual hyaline 

 valve was not observed, but it probably exists. 



This siphonal apparatus has the entire aspect of that of the 

 typical Tellinida; but its position when exserted is singular, 

 being very little posterior to the centre of the ventral range, in- 

 stead of being, as is more usual, protruded from a posterior 

 angle somewhat more basal, than a right one to a vertical line 

 drawn from the beaks to the ventral centre ; this nearly central 

 basal site is occasioned by the great size and low position of the 

 posterior adductor, which necessarily compels the issue I have 

 described. 



The foot is white, not large, flat, bevelled, pointed, very little 

 geniculated, without a byssal groove, scarcely differing from 

 the Tellina and some of the Veneres ; it also, from the causes 

 assigned to the siphons, has a more basal position than usual 

 when protruded, with a very limited anterior action, from which 

 it may be inferred that the motive power is confined to the turn- 

 ing from side to side and on its centre. The branchiae are sub- 

 circular, the upper plates being much less than the lower, half 

 lapping on them, pale drab, with moderately fine but not very 

 distinct pectinations ; the pair of palpi on each side are fleshy, 

 rather long, triangular, pointed, strongly pectinated on the out- 

 sides, smooth within, and connected with each other around the 

 mouth ; they are also light drab. The body is pale pink, small 

 and subglobular, having the foot fixed to its centre. The liver 

 is grass-green. 1 have already alluded to the texture of the 

 shell, but it is necessary to add, that in the right valve there are 

 two laminar primary teeth, and in the left two similar ones, with 

 a strong double tooth between them : there are no laterals. 



It would then appear, that the texture of the shell, the two 

 laminar teeth in the right valve, and the exact similitude to the 

 typical Telliiue, of the very long, slender, divergent siphonal ap- 

 paratus having each tube completely separated to the base, ally 

 this animal by many degrees nearer to the Tellinida than to the 

 Veneridce, as none of the genera of the latter family have any 

 resemblance to this siphonal condition; still it cannot be lost 

 sight of, that the three primary teeth in the left valve, which ap- 



