NATURAL SCIENCES OF PHILADELPHIA. 39 



to the genus Latrunculus of Gray, or Eburna of others.* The shell structure 

 appears to be more compact than in the typical Vivipari, and the species gen- 

 erally are more ponderous. The angulation of the outer lip and the sinus at 

 the base are characteristic, and contrast strongly with the uniform plane of 

 thp aperture of Viviparus. 



The figure of a <; deformed" V. decisa (36) published by Binney, gives an ex- 

 aggerated idea of this peculiarity of form. 



The soft parts of Melantho appear to also differ from those of Viviparus, the 

 rostrum being smaller and less protractile, and the auricles behind the tenta- 

 cles are likewise much smaller. 



The earliest known American species of Melantho were contemporaneous 

 with the Vivipari, three species having been discovered by Dr. Hayden in the 

 lignite beds of Fort Union and described by Meek and Hayden as Vivipara mul- 

 tilineala {=V. nebrascensis M. and H.), V. vetusta and Melania orLymnxa multi- 

 striata. These have now been referred to the genus Melantho in the manuscript 

 work of Meek and Hayden. 



Melantho multilineatus. 

 " vetustus. 

 " multistriatus. 



The following are referrible to the same genus, 3Ielantho: 



Melantho ponderosa Ad. ex Say = V. ponderosa B. 



" decisa Ad. ex Say = V. decisa B. 



" coarctata Gill ex Lea = V. coarctata B. 



" cyclostomatiformis Gill ex Lea = V. cyclostomatiformis B. 



" incrassata Ad. ex Lea = V. incrassata B. 



" decapitata Gill ex Anth. = V. decapitata B. 



" regularis Gill ex Lea = V. regularis B. 



LIOPLAX Troschel. 



Lioplax Troschel, Gebiss der Schnecken, p. 100, 1857. 



Haldemania Tryon, Proc. Acad, of Nat. Sciences, 1862, p. 451. 



Paludina sp. auct. 



Vivipara sp. auct. 



Shell imperforate or rimate, turreted, rather thick ; of very compact struc- 

 ture ; unprovided with colored bands ; whorls carinated and longitudinally flat- 

 tened, with the sides nearly parallel. Aperture little oblique, oblong-oval, 

 broadly rounded at the base, and sinuous or retreating backwards, the sharp 

 outer Up being subangulated near the front; columellar lip concave appressed 

 to the body whorl, forming an obtuse angle with the outer. 



Operculum corneous, with a large spiral nucleus, but with the subsequent 

 accretions concentric. 



This type is evidently most nearly related to Melantho, but differs especially 

 in the spiral nucleus of the operculum, as well as in the form of the aperture 

 A single species is found, which has been ascertained to inhabit some of the 

 streams of Ohio, Indiana, Kentucky, Pennsylvania and New Jersey. We are 

 indebted for its subgeneric distinction to Prof. Troschel and Mr. Tryon. 



Lioplax snbcarinata = Haldemania subcarinata = Vivipara subcarinata B. 

 ex Say. 



Note. I regret that I have not been able to avail myself more fully of the 

 invaluable " Gebiss der Schnecken" of Dr. Troschel. The four parts were only 

 received at the Smithsonian Institution, through the kindness of Prof. Agassiz, 



* The name of Latrunculus has been recently applied by Dr. Gunther to a genus of 

 Gobioid fishes, but, if no other reasons, cannot be retained on account of preoccupation 

 of the name. The genus had. however, previously received the name of Apkya from 

 Risso. 



1863.] 



