82 PROCEEDINGS OF THE ACADEMY OP 



DESCRIPTION OF TWO NEW FOSSIL SHELLS OF THE UPPER AMAZON. 



BY T. A. CONRAD. 



The Pebas group of the Upper Amazon was first discovered by 

 Prof. James Orton in 1867, who obtained a collection of the re- 

 markable shells, some of which were first described by Mr. Gabb. 

 Subsequently, at request of Prof. Orton, Mr. Hauxwell collected 

 other specimens, and Prof. Steere obtained some new species, 

 besides a very large number of several species of Pachydon. 

 Prof Orton, having revisited the region in which the Pebas group 

 occurs, has found two new forms which he has forwarded to me to 

 describe. These new shells belong to fresh-water genera, and help 

 to define the nature of the habitat of the gi'oup. They confirm 

 the opinion I advanced in the preceding paper, that it was a basin 

 of fresh water to which brackish water had access at times. The 

 Hemisinus herein described occurs crowded in the clay in such 

 perfection that the species must have lived and died on the spot, 

 and as the living shells of the genus inhabit fresh-water rivers of 

 South America, very far from salt water, they are as much fresh- 

 water shells as are those of Melania. Some of the shells are 

 water-worn, and there is abundance of small fragments of shells 

 in the claj^, in which respect it resembles some of the Miocene beds 

 of Virginia. The Pebas clay in all the localities is crowded with 

 specimens of Issea Orfoni, I. lintea, Liris laqiieata, all of which 

 I believe to be fresh-water shells of the family Melaniidse. 



The two shells described in this paper were found at Iquitos, 

 about 100 miles west of Pebas. 



Family UNIONID^. 



HAPLOTH^RUS, Conrad. 



Eqnivalve, hinge margin straight, the cartilage area very broad and thick, 

 hinge edentulous, anterior muscular scar small, narrow, and deeply 

 impressed, accessory situated under the primary scar. 



This is a large, very thick shell, laminated and pearly like Unio, 

 and is remarkable for the thick, broad hinge area. It comes in 

 fragments, so that the entire outline is unknown. The anterior 

 accessory scar is differently situated from that in Anodonta, 



