118 
This is the second example I have seen of this interesting species. 
A year since, I named, but did not publish it, after a smaller shell 
than the above in the Royal Museum at Berlin. This species is 
referable to the same section as D. exoleta, and is most allied to 
D. amphidesmoides of Reeve ; but it is very distinct in its form and 
sculpture, in its area, which is more impressed than in any related 
species, and particularly in its produced small triangular pallial 
sinus, which is rounded at the apex. The concentric striz are 
elevated and rounded in the middle of the shell, and diminish very 
much near the extremities ; in the posterior part there is a peculiar 
compression of the valves, at the place where the striz converge, 
whilst the latter suddenly turn upwards and become thinner by de- 
grees. 
2. Dostn1A TENELLA, Romer. OD. testa subquadrato-orbiculata, 
via longiore quam alta, tenui, translucida, compressiuscula, in- 
equilaterali ; lineis transversis densis, regularibus, postice vir 
convergentibus, et vix elevatioribus, superficie proinde serico 
simili nitente ; pallide ferrugineo-alba, umbonibus saturatioribus, 
mediocriter prominulis, acutiusculis, recurvis, longitudinem in 
ratione 1:2 dividentibus; margine ventrali semicirculari, ante 
et pone equaliter et valde ascendente; margine dorsali antico 
perbrevi, subrecto, obliquo, infra rotundatim prosiliente, postico 
declivi, producto, in marginem ventralem cum angulo rotundato 
transiente; lunula lanceolato-cordata, impressa, circumscripta, 
medio elevata; area subplana, angusta, ligamento subimmerso, 
sub labiis hiantibus conspicuo; intus albida, medio opaca; sinu 
palliari magno, triangulari, lineis includentibus rectis, in apice 
rotundato ; lamina cardinali tenui, angusta ; dente cardinali antico 
in valva sinistra tenui, obliquo, cum secundo, crassissimo complicato, 
dente lunulari mediocri, compresso. 
Long. 22, alt. 20°5, crass. 10°5 mill. 
Hab. Australia. 
In general appearance this small shell reminds one of D. subrosea 
Gray ; the shape is nearly the same, but the angle of the posterior 
end is more rounded than in that species, and the posterior slope 
more descending. The forms of the area and lunula are very different 
from those in D. subrosea, being not so much impressed, and the 
latter, which in D. subrosea is exactly heart-shaped, is in D. tenella 
more lanceolate. The concentric striz are so thin and regular as to 
produce an aspect like silk, whilst the strize in D. subrosea are flat 
and much broader. Besides the more solid growth of the latter, a 
most remarkable difference exists in the form of the pallial sinus, 
which in D. subrosea is broad and acute at the apex, while in D. 
tenella it is large and rounded at the top. In the latter the plate of 
the hinge is very small and thin. 
3. Dostn1A AMETHYSTINA, Rémer. JD. testa quadrato-rotundata, 
solida, compressiuscula, postice valde compressa, satis inequi- 
laterali; transversim lirata, liris equalibus, distantibus, filifor- 
mibus, extremitates versus confluentibus, striisque transversis 
