GONIOBASIS. 155 



to granulations as in Postellii. It is also near to caienaria, Say, from 

 South Carolina, but that shell is quite cancellate. I name this after 

 James Postell, Esq., of St. Simon's Island, to whom I owe the acqui- 

 sition of many fine mollusca, from Georgia. Pine specimens were 

 subsequently sent to me by Dr. Wilson, of St. Simon's Island, pro- 

 cured in Lewis' Creek. — Lea. 



This is a beautiful and rather common species — easily dis- 

 tinguished from all others belonging to this group. 



20. G. araclmoidea, Anthony. 



Melanin arachnoidea, Anthony, Ann. Lye. Nat. Hist. N. Y., vi, p. 95, t. 2, f. 14, 

 March, 1851. BiNXET, Check List, No. 19. Bkot, List, p. SI. Reeve, Monog. 

 Melania. pp. 83. 



.afe^a«iV^^)^<eriea;<a, Anthony, Proc. Acad. Nat. Sci., p. G2, February, 18G0. Bin- 

 key, Check List, No. 151. Brot, List, p. 34. Keeve, Monog. Melania, sp. 296. 



Description. — Shell conic, rather thin, horn-colored ; spire slender 

 and much elevated ; whorls twelve, very strongly striated and ribbed, 

 particularly the upper ones ; the ribs extend only to a 



r Ig 



prominent, acute carina on each whorl, situated below the 

 middle, between which and the suture below, one or two 

 coarse striae alone are visible, sutures deeply impressed ; 

 aperture very small, ovate, purplish within; columella reg- 

 ularly curved, without indentation, and with but a small, 

 very narrow sinus at base. 



Diameter, -28 inch (7 millim.) ; length, 1 inch (26 millim.). 

 Length of aperture -22 inch (2i millim.) ; breadth of aper- 

 ture, -15 inch (-1 millim.). 



Habitat. — A small stream emptying into the Tennessee River, near 

 London, Tennessee. 



Observations. — This is one of the slenderest and most elevated of 

 the genus ; more than forty specimens are before me, and they are 

 very constant in all their characters ; it comes nearest to M. striatula, 

 Lea, by its folds and stria3, but should not be confounded with it, being 

 different in every other particular; the number of whoi'ls is greater by 

 one-half, the striatula having only eight ; its proportions are altogether 

 more slender, the striatula standing as 21 to 49, while this is 28 to 100. 

 The present species is also much more folded and rough than the stri- 

 atula, Avhich is essentially a striate shell. Upon the older specimens 

 the folds are nearly obsolete on the two lower whorls, being there 

 coarsely striate only. About twelve stria; on the body-whorl and six 



