ANATINA. 145 
gamated single branchia, the invariable condition of all the 
Anatine ; 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 “convera.” 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,’ 1. p. 204, and iv. p. 250, of the Appendix. 
A. BIDENTATA, nobis. 
Montacuta bidentata, Brit. Moll. ii. p. 75, pl. 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 Clarkie 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 
Anatine, 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 
sth of an inch transverse, and not quite ;',th 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 
