123 
late lanceolata, superficiaria, medio elevata, e striarum transver- 
sarum processu crebro striata, linea subelevata vircumdata ; area 
lanceolata, subincisa, obtuse limitata; ligamento immerso, sub 
labiis late hiantibus conspicuo ; pagina interna alba, medio pallide 
luteo infecta ; sinu palliari magno, sublate aperto, apice acuto, 
lineis subconcavis incluso ; impressione musculari antica angusta, 
usque ad laminam cardinalem producta, postica latissime pyri- 
formi ; lamina cardinali angusta, tenui ; dente lunulari elevato, 
acutiusculo, valde remoto, dentibus cardinalibus tenuibus, secundo 
in valva dezxtra crasso, tertio permagno, perobliquo, bisulcato. 
Long. 37, alt. 35, crass. 20 mill. 
Hab. Malacca. 
This fine species belongs to the section represented by D. excisa 
of Chemnitz and D. trigona of Reeve; it differs from both not only 
in its thinner shell, the transverse strize of which are much finer, but 
still more in the following particulars. In D. excisa, the umbones are 
situated at 7, in D. trigona at 1, and in D. tripla at 2 of the whole 
length, so as to produce nearly the aspect of an isosceles triangle ; 
the ligament-area is very deeply excavated in the first, very narrowly 
lanceolate and but a little hollowed in the second, deeper and less 
narrowly lanceolate, but with rounded limits, in the third; the 
lunula is flat in D. ewcisa and trigona, being in the latter much 
broader than in the former, whilst it is swollen and convex in the 
middle, and mere lanceolate in D. tripla. The pallial sinus is broad 
and roundly triangular in both the former species, but less opened 
and acute at the apex in the latter, which has also a very thin and 
small hinge-plate. 
10. Dostnta pERupTA, Romer. D. testa rotundato-triangulari, 
subinequilaterali, tumidiuscula, tenuicula, vir latiore quam alta ; 
liris transversalibus regularibus, rotundutis, elevatis, interstitiis 
@quantibus, postice valde confluentibus cincta, interstitiis lirisque 
tenuissime transversim striatis ; pallide luteo-alba; umbonibus 
marginibus, lunulaque ut in D. tripla; area angustissime lanceo- 
lataesubexcisa, evacte ut in D. trigona; intus alba; sinu palliari 
latissime aperto, magno, apice acuto, lineis concavis incluso ; 
lamina cardinali angusta, subtenui ; cardine ut in D. tripla, sed 
dente cardinali medio in valva sinistra crassiore, tertio in dextra 
obsolete bisulcato. 
Long. 26, alt. 24, crass. 15 mill. 
Hab. Malacca. 
This species is nearly related to D. trigona; the outline is almost 
the same, the extremities being only a little more rounded. But the 
concentric striz, notwithstanding the smaller size of the shell, are 
far thicker, as broad as the insterstices, and, both being finely striated, 
produce the effect of smaller transverse strie. The ligament-area is 
formed exactly as in D. trigona. The pallial sinus is broadly open 
with an acute apex, the upper line being horizontally directed. From 
this it may be seen that D. derupta unites several of the characters 
of D. trigona and D. tripla; but the size, the sculpture, the pallial 
