ANATINA. 145 



gamated single branchia, the invariable condition of all the 

 Anatinae ; at least we judge so in respect of the present species 

 from a perfect dried animal, which, when saturated with 

 moisture, appeared to support this view ; and as regards the 

 A. convexa, though we have not seen it alive, we determine by 

 the analogy of several that have been examined. The contour 

 of the two is only slightly different in many young or dwarf 

 examples of the " convexa." In saying this we do not mean 

 to insist on identity. At any rate, enough surely has been 

 stated to convince, that the two are absolutely congeneric, and, 

 if not identical, they are all but so. For an account of the 

 animal of this Scotch production we refer to the ' British 

 Mollusca/ i. p. 204, and iv. p. 250, of the Appendix. 



A. BIDENTATA, noblS. 

 Montacuta bidentata, Brit. Moll. ii. p. 75, pi. 18. f. 6 & 6 a. 



We feel sufficiently confident to remove this species from 

 the modern genus Montacuta to Anatina : the distinct con- 

 cave subcircular ossicle, which we can show in specimens, and 

 the bi-angulation of the siphonal extremity - - the invariable 

 characteristic of Anatina left us no alternative ; indeed our 

 observations on Lepton Clarkice must have prepared mala- 

 cologists for this removal. I allude to the mention of the 

 ossicle, which is of such high authority as to require no 

 remarks with respect to position. Contrary to most of the 

 Anatince, the mantle of this animal is only closed posteally ; 

 but this exception shows the value we set on the preceding- 

 observation on the ossicle. 



Animal inhabiting a white shell, smooth at the umbones, 

 and often roughened at the margins with minute points, of 

 th of an inch transverse, and not quite T \jth vertical measure, 

 with prominent pointed beaks, of oval shape anteally, and sub- 

 angular posteally, which side is the shortest slope from the 

 beaks ; in the right valve, close on each side the ossicular and 

 cartilage-pit, is a strong triangular, flattish, acutely pointed 

 cardinal tooth; in the left valve the central pit is without 

 cardinals, but there are two rather distant obsolete laterals. 



L 



