Description of a new Exotic Melania. 

 BY GEORGE AV. TRYON, JR. 



Melania Helenve, Tryon, t. 1, f. 7. 



Desccription. — Shell turretted, whorls eight or nine, anp;ul<ated in the middle, 

 rather flattened abore, convex below, sutures deepl)^ impressed. Surface 

 spirally nodulously ridged, the nodules running into waved longitudinal ribs. 

 Aperture narrow, a little produced in front, contracted behind. Outer lip 

 sinuous, angulated in the middle. 



Dimensions. — Length 20 mill. Dlam. 8 mill. 



Ilab. — Philippine Islands, ily cabinet. 



Observations. — This shell is allied to Melania perfecla, Mousson, from Java, but 

 differs in being angulated, and in having a longer, narrower aperture; il is also 

 a little smaller and the apicial whorls are sculptured, not smooth. Since the 

 above description was written, I have observed iu the collection at the Academy 

 fine specimens of Melania Mauicnsis, Lea, the sculpturing of which somewhat 

 resembles this species, but they are much stouter, more obtuse shells, with the 

 periphery not angulated. 



Descriptions of new Species of Fresh Water Mollusca, belonging to the 

 Families AMNICOLID.a;, VALVATID.ffi and LIMN.ffiIDiE ; inhabiting Cali- 

 fornia. 



BY GEO. AV. TRYON, JR. 



The following species of Shells seat to me by my friend Mr. Wm. M. Gabb, 

 were principally collected by Rev.J.Rowell, of San Francisco, — a gentleman whu 

 has devoted much time to the studj^ of the Mollusca of the State of California. 



It is not without considerable hesitation that I propose new species in genera 

 wherein the variations of form, due to climatal aud othir inflaeaces, are so 

 great, and where the geographical distribution is frequently so extended ; and 

 it is only after very extensive comparisons with the related species .which have 

 already been characterized, that I select for description those among the suite 

 sent to me which appear to be most distinct, leaving others unnamed, until a 

 more extended exploration of the State shall give us a more perfect knowledge 

 of the extent and relations of the Molluscous fauna inhabiting its waters. 



A considerable number of shells belonging to the above families, appear to 

 inhabit the entire breadth of the continent ; adding to these the forms ascer- 

 tained to be peculiar to Oregon and California, we find already decided indica- 

 tions that these States form the metropolis of the fresh-water Pulmono- 

 branchiates of North America. 



I have added to the descriptions of new species, a list of those alreadv 

 described, which have been sent to me by Mr. Gabb, because, in most case?, 

 the localities are new and interesting. 



AMNICOLID.E, Tryon. 



1. Ajimcola Rowellii, Tryon, t. 1, f, 8, 9. 



Description. — Shell depressed, wider than high, consisting of three and a 

 half whorls, which are regularly convex and rapidly enlarging; spire small, 

 but little elevated, apes acute, sutures well marked; base convex, except that 

 the region surrounding the umbilicus is flattened and inclining towards the 

 axis, its outer boundary, consequently, is marked by an angle ; umbilicus small 

 but very distinct ; aperture half ovate, the labrum well rounded and thin, the 

 labium but slightly rounded, thickened, elevated from the body-whorl, forming 

 an acute angle with the labrum above, and not impinging on the umbilicus'. 

 Surface marked with close, regular, minute striae, which become enlarged in 



