207 



Unio apiculatus. — Desc. SlicU subquadrate, the diametei> 

 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 apiculatus, nob. " Disseminator," 1829. 



Unio asper. 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 

 GnatJiodon truncatus, Lam., (Cy-e^ict) 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, Raf , but the surface is in every part 

 ornamented with crouded, elevated, more or less rounded tubercles, 

 not very difi"erent 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 apiculatus may be 

 considered as a variety only of the quadrulus. PI. 52. 



Unio quadrulus, Raf. — Specific character. Shell subquad- 

 rate, tuberculated, with a nodulous ridge and dilated groove. 

 Unio quadrulus, Raf. Ann. gen. des Sci. Phi/s., vol. 5. 



