207 
Unio apiculatus. — Desc. Shell subquadrate, the diameters 
being subequal ; summits not very prominent : hinge margin de- 
clining, and with the anterior margin compressed and separated by 
an obtuse angle ; anterior margin generally retuse ; basal margin 
retuse before the middle ; posterior margin rounded ; disk with a 
costa from the summit descending to the anterior basal angle, 
which is somewhat prominent and rounded ; behind the costa is a 
much dilated groove, not very deeply impressed ; the whole sur- 
face, without exception, is studded with small, subequal eminences, 
which are more or less rounded or transverse and arranged more or 
less symmetrically in lines, which, before the costa, curve towards 
the ligament and anterior margin, are angulated in the groove and 
on the middle, and thence are arquated towards the posterior mar- 
gin ; within pearly white, iridescent before ; anterior accessory 
cicatrix confluent; posterior accessory cicatrix small, hardly dis- 
tinct, rounded. 
Unio apiculatuSj noh. Disseminator 1829. 
Unio asjper. Amer. Philos. Trans. , 1832. 
Ohs. I obtained a few single valves of this handsome species, 
from a large quantity, consisting of many wagon loads, of the 
Gnathodon truncatus, Lam., ( at New Orleans, during a 
short sojourn in that city with Mr. Maclure in 1827. This vast 
heap of dead and bleached shells, had been collected on the shore 
of Lake Ponchartrain, and conveyed by means of small vessels 
through the canal, for the purpose of covering part of the levee ’’ 
of that city, as a substitute for a pavement. I have subsequently 
received several good specimens from my friend Mr. Barabino. 
In general outline and form of the disc, it has a very close re- 
semblance to U. quadridus, Baf, but the surface is in every part 
ornamented with crouded, elevated, more or less rounded tubercles, 
not very different in point of size, and symmetrically arranged in 
angulated and arquated series. Notwithstanding these differen 
tial traits, I think it not improbable that when we shall become 
better acquainted with this Protean genus, the apicidatus may be 
considered as a variety only of the quadridus. PI. 52. 
Unio quadrultjs, Baf — Specific character. Shell subquad- 
rate, tuberculated, with a nodulous ridge and dilated groove. 
Unio quadrulus, Raf. Ann. gen. des Sci, Phgs., vol. 5. 
